FR: git diff ignore option

[Thomas Wolff <towo@xxxxxxxx>]

git diff is missing an ignore option, like `diff -I`, which would be 
especially useful for translation files (.po) to check changed contents 
and not updated line numbers:

#: sourcefile.c:/123/
msgid "id"
msgstr "*changed text*"

"changed text" is important to be checked, "123" is distracting

Kind regards
Thomas