Log Message:
Update to 2.6.3:

This is a regularly-scheduled bugfix release.

    commit: amending with --close-branch (issue3445)
    doc: make it easier to read how to enable extensions
    doc: reword "config file" to "configuration file"
    docs: change description to synopsis in hgrc.5
    histedit: raise ImportError when demandloading is enabled
    pathencode: fix hashmangle short dir limit (issue3958)
    update: remove .hg/graftstate on clean (issue3970)