Make combinePathAndFile() return char * instead of vString

Make combinePathAndFile() return char * instead of vString

Also move eStrdup() to the correct position in the header.

In addition add the same includes into debug.h as those in uctags (the
removal of vstring inclusion inside routines.h causes compilation errors -
it would be best to explicitly include all needed files in every source to
avoid problems like this but let's do just syncing the two implementations
for now).