tests/test-issue1175

templatefilters: add new stripdir filter

Adds a new template filter for removing directory levels from a
string. Examples:

{foo|stripdir} -> 'foo'
{foo/bar|stripdir} -> 'foo'
{foo/bar/more|stripdir} -> 'foo/bar'
{foo/bar/more|stripdir|stripdir} -> 'foo'

#!/bin/sh
rm -rf a
hg init a
cd a
touch a
hg ci -Am0
hg mv a a1
hg ci -m1
hg co 0
hg mv a a2
hg up
hg ci -m2

touch a
hg ci -Am3
hg mv a b
hg ci -Am4 a
hg ci --debug --traceback -Am5 b
hg verify
hg export --git tip