templater: add context.preload(t) to test if the specified template exists
I'm going to remove 'templ' from the resources dict because it is the only
resource that the caller can't provide. This also implies that putting
'templ' into the resources dict creates a reference cycle.
context.preload(t) will be used in place of templater.__contains__().
$ hg init
$ echo "added file1" > file1
$ echo "added file2" > file2
$ hg add file1 file2
$ hg commit -m "added file1 and file2"
$ echo "changed file1" >> file1
$ hg commit -m "changed file1"
$ hg -q log
1:08a16e8e4408
0:d29c767a4b52
$ hg id
08a16e8e4408 tip
$ hg update -C 0
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg id
d29c767a4b52
$ echo "changed file1" >> file1
$ hg id
d29c767a4b52+
$ hg revert --all
reverting file1
$ hg diff
$ hg status
? file1.orig
$ hg id
d29c767a4b52
$ hg update
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg diff
$ hg status
? file1.orig
$ hg id
08a16e8e4408 tip
$ hg update -C 0
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ echo "changed file1" >> file1
$ hg update
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg diff
$ hg status
? file1.orig
$ hg id
08a16e8e4408 tip
$ hg revert --all
$ hg diff
$ hg status
? file1.orig
$ hg id
08a16e8e4408 tip
$ hg revert -r tip --all
$ hg diff
$ hg status
? file1.orig
$ hg id
08a16e8e4408 tip
$ hg update -C
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg diff
$ hg status
? file1.orig
$ hg id
08a16e8e4408 tip