Move AM_clearMarks call into P_InitNewLevel with other "subsystem wake up" code.

git-svn-id: http://mancubus.net/svn/hosted/eternity/trunk@2873 86ba831e-150c-0410-ab35-e06eaae15ed9
* Added P_CheckLevelName and P_CheckLevelMapNum variants of P_CheckLevel function
* Reformatted isMAPxy and isExMy macros
* Use ectype::isDigit in translation parser
* Potential bug fix in translation parser: do not I_Error in qstring::operator [] if length is 0
* Bit of C++ cleanup in w_levels

git-svn-id: http://mancubus.net/svn/hosted/eternity/trunk@2874 86ba831e-150c-0410-ab35-e06eaae15ed9