[MP] Fix stack corruption after 761e55fd73

After reducing the size of the char buffers in WP_InitForcePowers, the
server crashed due to stack corruptions. This was a result of
BG_LegalizedForcePowers assuming that the char buffer handed to it (which
in this case was one of the buffers reduced in size) was at least 128
bytes in size. A string copy was then performed, which corrupted the
caller's stack.

This commit adds an extra parameter to BG_LegalizedForcePowers for the
size of the passed in buffer.
[MP] Fix #468 - using wrong team model colour

This commit fixes a small bug where you could use the other team's colour
for player skins.
[MP] Remove unnecessary assertion in skin loading.
[MP] Added useful error messages for DLL loading

This commit adds some additional error reporting messages when failing to
load DLLs. This is in addition to the 'dll failed to load' errors which
provided no useful information.