Replaced version comparison function

Fix for OSX error message:

    expr: not a decimal number: '1'
Readlink and realpath doesn’t exists and/or has different argument flags

In OSX readlink has different arguments and realpath doesn’t exists.
These commands where being used to determine the absolute physical path
of a file. It is not necessary to use these commands to do this. Instead
a abs_path function has been created that uses pwd, basename and
dirname.
Merge pull request #33 from wesclemens/master

Missing commands in OSX
Add some links to the TOC
Auto-download of shunit2 when running tests
Fix logging bug when `symlink` creates a directory
Fixed missing dot in documentation (my bad)
Merge pull request #35 from fenekku/master

Fixed missing '.' in documentation for use of homeshick on other machines
Do not resolve path in abs_path.
We used to do that with realpath in `track', but it wasn't really the intention.
It could make perfect sense if a user wanted to track a symlink in $HOME
that links to somewhere else in the system.
By resolving the symlinks we disallowed that.
No need to use the `err` function, abs_path is internal
Simplify abs_path
Simplify abs_path even further
add symlink directory check impl and test
Fix shunit downloading with curl
avoid using readlink
symlink_cloned_files() now working on OSX
stat() fallback in test/track.sh/testNOverwrite()
Generate castle names in sorted order

The 'find' command outputs castles in an arbitrary order, which can be
annoying in some cases (e.g., when listing all castles and trying to find
a particular one by sight).
Merge pull request #36 from jjlin/contrib

List castle names in sorted order
Merge remote-tracking branch 'upstream/master'

Conflicts:
	utils/git.sh