Added --with-irods=/path/to/irods option to configure.

Updated the README and manuals for recent user-visible changes.
Updated to use --with-irods=$IRODS_HOME
Set the IRODS_HOME explicitly.

Added DISTCHECK_CONFIGURE_FLAGS to pass iRODS location to make
distcheck.
Merge pull request #93 from keithj/devel

Improvements to build and updates to README and manual.