Soft link frameworks into /usr/local/lib

This fixes the case when the user is not using a default homebrew
install (e.g. when on boxen).

As opposed to just telling the user what to do, we let the computer do
it, turns out they're pretty good at that.
Don't claim that everything is a lib.
Use -p with mkdir.
Make the linking status message more obviously our output
No need to throw all these quotes in.

lolbash.
Quote the paths.
Force the symlink creation.
Only link libssh2.a.
Check for presence of the target.
Merge pull request #259 from libgit2/fix-non-default-homebrew

Soft link frameworks into /usr/local/lib