sage -b fails after touching sage/libs/mwrank/{mwrank.pyx,wrap.cc}

[cremona]

1. Make a fresh clone of a 3.0.2 build.
2. touch $SAGE_ROOT/devel/sage-test1/sage/libs/mwrank/mwrank.pyx
3. sage -b
4. touch $SAGE_ROOT/devel/sage-test1/sage/libs/mwrank/wrap.cc
5. sage -b

...produces this:

----------------------------------------------------------
sage: Building and installing modified SAGE library files.


Installing c_lib
scons: `install' is up to date.
running install
running build
running build_py
running build_ext
building 'sage.libs.mwrank.mwrank' extension
error: unknown file type '.pyx' (from 'sage/libs/mwrank/mwrank.pyx')
sage: There was an error installing modified sage library code.

but then after doing again

touch $SAGE_ROOT/devel/sage-test1/sage/libs/mwrank/mwrank.pyx

sage -br works fine.

[mabshoff]

For the record: #3491 is a dupe of this and I closed the other ticket.

Cheers,

Michael

[mabshoff]

This ticket has been fixed via Craig's and Gonzalo's patch at #4480.

Cheers,

Michael