[with patch; positive review] optimize sage startup: don't import sympy by default

[was]

The attached patch works and speeds up the sage import from between 0.1 and 0.5 seconds, depending on caching.

NOTE: It is necessary to fix a bug in sympy first.

11:57 < wstein> The fix would be to change line 99 of printing/pretty/pretty_symbology.py to
11:57 < wstein>             try:
11:57 < wstein>                encoding = sys.stdout.encoding
11:57 < wstein>             except AttributeError: return
11:58 < wstein> Yep, that 100% fixes the problem.
11:58 < ondrej> ok, I'll commit it. thanks
11:58 < wstein> Maybe you already did that?
11:58 < wstein> It is right, I think, since you do almost the same thing 2 lines later.

[was]

To verify that this indeed fixes the "sympy gets imported" problem, do this:

teragon-2:calculus was$ sage -startuptime |grep sympy teragon-2:calculus was$

after applying the startuptime patch: #3559

[was]

This bug is fixed in the new version of sympy:

12:01 < ondrej> now it is not
12:01 < ondrej> we fixed that in 0.5.15
12:01 < ondrej> bug I fixed important bug in our hg
12:01 < ondrej> and I am releasing the whole weekend...
12:02 < ondrej> (important sage<-> sympy bug)
12:02 < ondrej> so when I release, I'll create a spkg

[certik]

Thanks for the bug report. This is fixed in sympy 0.5.15. Sympy 0.5.16 that is about to be released tomorrow fixes another important bug with sympy matrices in Sage, so I'll create a new spkg tomorrow, or on Tuesday the latest.

[certik]

A new sympy-0.6.0.spkg together with a patch for sage was attached to #3592.

[mabshoff]

The does what it advertises, "testall long" passes with the patch applied. Positive review.

Cheers,

Michael

[mabshoff]

Merged in Sage 3.0.6.alpha1