Apply srb2home path to EXEC, SAVECONFIG, and debugfile

srb2home was missing from EXEC, SAVECONFIG, and debugfile, so those commands would look in the improper folders for Mac and Linux (and Windows, if %userprofile%\SRB2 was being used. To test, move config.cfg to that path.)

Tests well with srb2home set to SRB2 install path as well as user profile folder.

It's worth noting that file finding is a MESS in the current code, and not at all centralized... I'm pretty sure these three cases are the only ones not already handled with srb2home.