Shadowing conflict checks on enable toggle

[trialq]

How about whenever a mod gets enabled, its files are checked against all already enabled mods? The only file that should safely be present in both is the modinfo file, if there are any other matches it's almost certainly a shadowing conflict. PAMM should warn the user that there is a conflict, giving them a choice whether to enable the mod or not.

This would most help server mods, most of which rely on shadowing alone. There are 6 server mods currently on PAMM which shadow base_commander; only two mention commanders in their name or description, and even then it's not obvious that these mods conflict.