largefiles: introduce "_lfcommithooks" to abstract pre-committing procedures
This changes allows to customize pre-committing procedures according
to conditions.
This patch uses "stack" with an element instead of flag like
"_isXXXXing" or so, because:
- the former works correctly even when customizations are nested, and
- ensuring at least one element can ignore empty check
workingfilectx.date = (1000, 0)
ASCII : Gr?ezi!
Latin-1 : Grüezi!
UTF-8 : Grüezi!
<status modified=['foo'], added=[], removed=[], deleted=[], unknown=[], ignored=[], clean=[]>
diff --git a/foo b/foo
--- a/foo
+++ b/foo
@@ -1,1 +1,2 @@
foo
+bar