revert depend for non-gem build
build PGPLOT automatically
add --exclude and .gitignore
setenv PGPLOT_DIR for auto-build lib
new file: extconf-auto.rb
set PGPLOT_DIR if autobuild
change autobuild scheme; autobuild through Makefile
improve dependencies for autobuild
minor fix
trim no-use
check fortran compiler in extconf-auto.rb
minor fix
gem version
do not ext/rb_pgplot.c in gem because gem 1.8.23 fails to bundle it
0.1.9: update collapsed gem
Add --enable-autobuild option

This enables the automatic download and build of the pgplot library only if the
user provides the --enable-autobuild option.  This is more security conscious
as it requires the user's explicit permission (by providing --enable-autobuild)
to download and install this third party library.
Add --disable-extra-libs option

Some PGPLOT installations have incompletely linked PGPLOT libraries so linking
against libcpgplot requires also linking against other libraries such as
libpgplot, libX11, libpng, etc.  These extra checks are mostly benign for
PGPLOT installations that don't need them, but they can cause problems.
For example, mkmf uses "gcc" when checking for the Fortran libraries, but the
resulting Makefile uses "cc" when linking.  If "cc" uses a different library
path than "gcc", it is possible for the check to succeed but the link to fail.
This might have been due to a weird combination of factors in my system
(e.g. custom Ruby build using gcc installed via MacPorts and MacOS's cc), but
if it happened to me it could happen to others.  Adding the --disable-extra-lib
option provides a solution for this case.
Close files in cogen.rb

This is important for running cogen.rb from within Rakefile.  Without
explicitly closing the output file, a truncated version of rb_pgplot.c
may be packaged in the gem file before the rb_pgplot.c file gets closed
when the rake process exits.
Be smart about extra library checks

Try to find libcpgplot before looking for extra libs like x11, gfortran,
png, etc.  If the initial check for libcpgplot fails, then look for the
extra libraries and re-check for libcpgplot.  This removes the need for
the --enable-extra-libs option.