magit-locate-emacsclient: kludge for multi-arch Emacs for Mac OS X
magit-commit-add-log: Use symbol boundary in function name REGEXP

Use symbol boundary instead of word boundary in function name REGEXP. This is
because using word boundary causes partial function name being matched. As an
example, let's say we have two diff hunks, one in the function `foo' and the
other in `foo-bar'. When the word boundary REGEXP is used, the REGEXP matches
both function name `foo' and `foo-bar', which will prevent
`magit-commit-add-log' from adding a log entry for function `foo-bar' if an
entry for function `foo' already exist.
Add a defcustom for `magit-status-mode-hook'.

This will allow users to customize it and extension packages, such as
magit-filenotify, to use `custom-add-option' to add themselves as option
to it.
Add `magit-load-config-extensions' option to `magit-mode-hook'.

This will make it easier and more noticeable when customizing magit.
Add options for stgit, svn, topgit to `magit-mode-hook'.

This will make them more noticeable when customizing magit and easier to
enable.
Merge pull request #1455 from YorkZ/bug-fix

magit-commit-add-log: Use symbol boundary in function name REGEXP
Merge pull request #1456 from ruediger/customhookoptions

Provide options for `magit-mode-hook`