Add conflicts option for Portfiles

[blb@…]

Attached is a patch (rooted in trunk/base) to add a conflicts option to Portfiles, to allow ports to indicate that they conflict with another port (or ports).

The basic idea is like dependencies:

conflicts   port:portname

to both allow ease of use through familiarity and in case we want to add other options besides port: in the future.

I'm not sure how best to handle what port should do when this occurs. With the current, patch, port simply exits with an error:

Error: Unable to execute port: Can't install dvdrtools because conflicting ports are installed: cdrtools

(I updated dvdrtools to have "conflicts port:cdrtools" for testing). This only occurs if the conflicting port is active (for image mode) or simply installed (for direct).

I also thought about maybe showing a message that "this port will fail to install/activate because conflicting port xyz is installed/active".

[blb@…]

diff (in trunk/base)

[jmroot (Joshua Root)]

Committed a modified version in r51525. Most importantly, the check is done in mportdepends, so for port install, the conflict is detected before anything gets installed. Upgrade (as usual) presents its own special challenge, since it installs one port at a time.

[blb@…]

The option was added in r51510.