Fix CHttpStream.bas
Was doing a 'string = *byte ptr' assignment, which has been disallowed now.
Cast to zstring ptr first for same effect.
makefile: Remove unused AS variable
makefile: Fix reference to fbc-new
makefile: Rename *.o dir variables to use more sensible names
makefile: Assume mkdir -p works

The makefile isn't trying to be compatible to mingw32-make/cmd.exe for
a long time now, so it may aswell make use of mkdir -p which is
available under Linux, MinGW/MSYS, and also DJGPP.