subrepo: fix subrelpath for git subrepos
This patch conforms gitsubrepo code to the variable naming scheme of the other
subrepo implementations. All user-facing path references should be relative
to the root repository.
$ hg init
$ python -c 'print "confuse str.splitlines\nembedded\rnewline"' > a
$ hg ci -Ama -d '1 0'
adding a
$ echo clean diff >> a
$ hg ci -mb -d '2 0'
$ hg diff -r0 -r1
diff -r 107ba6f817b5 -r 310ce7989cdc a
--- a/a Thu Jan 01 00:00:01 1970 +0000
+++ b/a Thu Jan 01 00:00:02 1970 +0000
@@ -1,2 +1,3 @@
confuse str.splitlines
embedded\rnewline (esc)
+clean diff