Parse user crontab

[gregorg]

Add the ability to parse user crontabs: https://code.google.com/p/chkcrontab/issues/detail?id=2

[lyda]

Yes, saw that and saw I was too late to migrate issues. :(

But this works as a way to do it! Good idea. I've committed my home dir to a VCS for a long time - subversion, hg and now use vcsh as a wrapper around git. And I recently put in a way to maintain a user crontab per-machine. Having this would be a nice addition. Adding a vcsh hook to check crontabs before commits would save some screwups.

This will be a little tricky as the name issue is just part of it. I'll address that partially in #4.

What I think makes the most sense would be to add a -u option where it would ignore the file name and have it skip usernames.