New option: -x

Removes the current directory from the data file.

Use case: sometimes `z tmp` lead me to `/tmp` whereas I was expecting to
be in `~/tmp`, with the new option I can do `z -x tmp`: it removes
`/tmp` from the data file and jumps to `~/tmp`.
Merge pull request #94 from baskerville/prune-pwd

New option: -x
Fix a few typos
Regenerate README from man page

Closes #97
Merge pull request #98 from baskerville/fix-typo

Fix a few typos
Throw away tmp files if mv fails

Attempt to get rid of stale temp files that occasionally drop. While
there is anecdotal evidence that this doesn't solve the problem, it
doesn't hurt, and it's the only place I can see to fix it.
revert warning if z.sh is being exec'd and not sourced

Because we can't reliably determine if we're really being exec'd.
Merge branch 'master' of git://github.com/rupa/z

Conflicts:
	README
	z.1
	z.sh