Fix Boyer Moore Nocase bug where BoyerMooreCtxToNocase was missing.

Whenever DETECT_CONTENT_NOCASE is set for a BoyerMoore matcher, the
function BoyerMooreCtxToNocase() must be called. This call was missing
in AppLayerProtoDetectPMRegisterPattern().

Also created BoyerMooreNocaseCtxInit() that calls BoyerMooreCtxToNocase()
to make some code cleaner and safer.