Remove tests that fail under CPython 3.5

See http://bugs.python.org/issue19995 for rationale. As micropython currently
aims for Python 3.3 compatibility I have not changed behaviour, but this
change allows the test suite to be run against a newer Python without having
spurious failures.
Merge pull request #663 from Rosuav/floatpercentx

Remove tests that fail under CPython 3.5
Change comments (mainly URLs) to no longer specifically say Python 3.3
py: Small changes to objstr.c, including a bug fix.

Some small fixed:

- Combine 'x' and 'X' cases in str format code.

- Remove trailing spaces from some lines.

- Make exception messages consistently begin with lower case (then
needed to change those in objarray and objtuple so the same
constant string data could be used).

- Fix bug with exception message having %c instead of %%c.
Merge pull request #665 from Rosuav/naming3.3

Change comments (mainly URLs) to no longer specifically say Python 3.3
py: Raise TypeError when trying to format non-int with %x,%o,%X.

This behaviour follows Python 3.5 standard (in 3.4 it's a
DeprecationWarning which we'd rather make a TypeError).
modgc: Implement return value for gc.collect(), enable on Unix.
modgc: 64-bit cleanness.
modgc: Real 64-bit cleanness.
Merge remote-tracking branch 'upstream/master'
Some more alloca() fixes for FreeBSD
Use libdl only on Linux for now. FreeBSD provides dl*() calls from libc
Some more alloca() fixes for FreeBSD