initial pass at automake and autoconf
automake and autoconf support

- refactored configure.ac to perform realistic tests and test for the pam,
  json, and curl libraries and headers
- refactored Makefile.am to build the correct module filename and a
  command-line test program
- added sptest.c for command-line testing
- added all the autoconf and automake cruft to .gitignore
- renamed config.[ch] to spconfig.[ch], since config.h conflicts with
  autoconf's config.h
- added autogen.sh
removed usunsed variable