.hgignore

hgmerge: add and use more tool variables

This patch adds even more customisable variables with tool paths.
Also moves $FILEMERGE where it belongs.

syntax: glob

*.elc
*.orig
*.rej
*~
*.so
*.pyc
*.swp
*.prof
tests/*.err
build
dist
doc/*.[0-9]
doc/*.[0-9].{x,ht}ml
MANIFEST
patches
mercurial/__version__.py

syntax: regexp
^\.pc/