Add automatic binary file detection to diff and export
Based on a patch by Fuming Wang
- add util.binary which decides whether a file is binary if it has any NUL
characters in the first 1K.
- teach mdiff.unidiff to print "binary file <x> has changed" for binary files
- add text flag to cause unidiff and dodiff to treat all files as text
- add -a and --text flags (like diff(1)) to hg diff and export
- update docs
\.elc$
\.orig$
\.rej$
~$
\.so$
\.pyc$
\.swp$
\.prof$
^tests/.*\.err$
^build/
^dist/
^doc/.*\.[0-9](\.(x|ht)ml)?$
^MANIFEST$
^\.pc/
^patches/
^mercurial/__version__.py$