extend mercurial plugin to be more like git/svn

implement in_hg(), hg_get_branch_name(), hg_prompt_info(), and hg_dirty() for the mercurial plugin
named functions similar to subversion plugin, to give theme maintainers an easier life
Fixed missing retcode function
Uncomment l alias
Change sublime text path select priority on mac.

User changed symbolic link for sublime binary is now top priority,
since this allows users to actually specify which version of sublime
they want to use. Sublime text 2 binary has higher priority over
sublime text (3) binary, since sublime text 2 is considered more
stable.
eliminated unnecessary cd and failing substitution

Changing the working directory in a sub-subshell
does not change the working directory of the executing
shell.

The substitution was broken for me on _all_ my machines,
so I started looking into the business.
Cache for fasd --init

Using cache technique for faster fasd --init as shown at:
 https://github.com/clvv/fasdi#install
Merge pull request #1779 from lorn/fasd_update

Cache for fasd --init
Merge pull request #1774 from kevinxucs/sublime-default-2

Change sublime text path select priority on mac.
gentoo linux support
Merge pull request #1803 from bebugz/patch-1

gentoo linux support
helpful changes to mysql, etc.
Adding a fix for the DISABLE_UNTRACKED_FILES_DIRTY option.
Add web-search plugin.

This plugin adds google, bing and yahoo commands to launch the default
web browser to do web search:

e.g.

    google oh-my-zsh
    bing what is zsh
Fixed recursion. Git not needed for it to work.

Avoid infinite `cd` loops under certain conditions. Try getting `.venv` from the current directory (not necessarily always using git)
Merge pull request #1839 from Kronuz/patch-1

Fixed recursion. Git not needed for it to work.
Merge pull request #1837 from xuhdev/web-search

Add web-search plugin.
Merge pull request #1775 from marcusmueller/fixupgradetool

fix for failing substition & eliminated unnecessary cd
Merge pull request #1834 from croach/disable_untracked_files_dirty_fix

Adding a fix for the DISABLE_UNTRACKED_FILES_DIRTY option.
fix the open command in linux using xdg-open
Merge pull request #1849 from lemieux/master

Fix for Jira plugin on Linux