Drop "-p -o root -g root" from the INSTALL_* Makefile variables and honor
the CONF Makefile variable for accessing the global config file instead of
hardcoding it as /etc.
These changes allow users without root access to install wmcalc in their home
directory.
In particular,
- Drop INCLUDES and LIBINC variables; referenced deprecated X11R6 directories
and INCLUDES unnecessarily included the default path.
- Switch hard-coded gcc for CC variable.
- Move hard-coded -02 and -Wall flags to new CFLAGS variable.
- Switch ${} to $() for consistency.
- Add new INSTALL_DIR variable for creating installation directories.
- Respect CPPFLAGS and LDFLAGS.
