Next round of minor compiler warning fixes. * include/internal/ftrfork.h (FT_RFork_Ref): Change `offset' member type to `FT_Long'. (CONST_FT_RFORK_RULE_ARRAY_BEGIN): Add `static' keyword. * include/internal/ftstream.h (FT_Stream_Pos): Return `FT_ULong'. * src/base/ftoutln.c, src/base/ftrfork.c, src/base/ftstream.c: Signedess fixes.