Merge branch 'cw/help-over-network'

Merge branch 'cw/help-over-network'

"git help -w $cmd" can show HTML version of documentation for
"git-$cmd" by setting help.htmlpath to somewhere other than the
default location where the build procedure installs them locally;
the variable can even point at a http:// URL.

* cw/help-over-network:
  Allow help.htmlpath to be a URL prefix
  Add config variable to set HTML path for git-help --web