Mark morphisms as coercions

[roed]

Currently, DefaultCovertMaps have an attribute _is_coercion that is unused. I propose moving it up to Map and setting it when coercion maps are created.

[roed]

New commits:

​6be53f3

Move _is_coercion from DefaultConvertMap to Map and make it accurate

[roed]

Just ran tests: they all pass.

[saraedum]

Looks good except for one "Conversion map" that should print as a "Coercion map".

[saraedum]

New commits:

​7dac7e2	Fix doctest
​9a9e437	Print default "coerce" maps as "Coercion"
​d8eec2d	Fixed doctests

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​2fa81a7

Fix doctests to print exactly as they show up on screen

[vbraun]

Merge conflict

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​b483c8e

Merge branch 'develop' into t/23211/mark_morphisms_as_coercions

[saraedum]

Fairly trivial merge conflict. Let's wait for the patchbot just to be safe.

---

New commits:

​b483c8e

Merge branch 'develop' into t/23211/mark_morphisms_as_coercions

[roed]

I just ran tests: they all pass.

[vbraun]

sage -t --long --warn-long 73.0 src/doc/en/thematic_tutorials/coercion_and_categories.rst
**********************************************************************
File "src/doc/en/thematic_tutorials/coercion_and_categories.rst", line 826, in doc.en.thematic_tutorials.coercion_and_categories
Failed example:
    P1.coerce_map_from(P2)
Expected:
    Conversion map:
      From: Multivariate Polynomial Ring in w, v over Integer Ring
      To:   Multivariate Polynomial Ring in v, w over Rational Field
Got:
    Coercion map:
      From: Multivariate Polynomial Ring in w, v over Integer Ring
      To:   Multivariate Polynomial Ring in v, w over Rational Field
**********************************************************************
1 item had failures:
   1 of 192 in doc.en.thematic_tutorials.coercion_and_categories
    [191 tests, 1 failure, 0.72 s]
----------------------------------------------------------------------
sage -t --long --warn-long 73.0 src/doc/en/thematic_tutorials/coercion_and_categories.rst  # 1 doctest failed
----------------------------------------------------------------------
Total time for all tests: 2.1 seconds
    cpu time: 0.7 seconds
    cumulative wall time: 0.7 seconds

and

sage -t --long --warn-long 73.0 src/doc/en/reference/coercion/index.rst  # 1 doctest failed
Running doctests with ID 2017-06-17-14-11-34-0b4119bb.
Git branch: develop
Using --optional=mpir,python2,sage
Doctesting 1 file.
sage -t --long --warn-long 73.0 src/doc/en/reference/coercion/index.rst
**********************************************************************
File "src/doc/en/reference/coercion/index.rst", line 223, in doc.en.reference.coercion.index
Failed example:
    cm.explain(ZZ['x','y'], QQ['x'])
Expected:
    Coercion on left operand via
       Conversion map:
         From: Multivariate Polynomial Ring in x, y over Integer Ring
         To:   Multivariate Polynomial Ring in x, y over Rational Field
    Coercion on right operand via
       Conversion map:
         From: Univariate Polynomial Ring in x over Rational Field
         To:   Multivariate Polynomial Ring in x, y over Rational Field
    Arithmetic performed after coercions.
    Result lives in Multivariate Polynomial Ring in x, y over Rational Field
    Multivariate Polynomial Ring in x, y over Rational Field
Got:
    Coercion on left operand via
        Coercion map:
          From: Multivariate Polynomial Ring in x, y over Integer Ring
          To:   Multivariate Polynomial Ring in x, y over Rational Field
    Coercion on right operand via
        Coercion map:
          From: Univariate Polynomial Ring in x over Rational Field
          To:   Multivariate Polynomial Ring in x, y over Rational Field
    Arithmetic performed after coercions.
    Result lives in Multivariate Polynomial Ring in x, y over Rational Field
    Multivariate Polynomial Ring in x, y over Rational Field
**********************************************************************

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​78807fa

fix doctest errors

[chapoton]

you introduced a bad trac role, please review #23526

[roed]

Replying to chapoton:

you introduced a bad trac role, please review #23526

Oops! Sorry about that.