This macro searches for a program called 'pgclient'.
If found the variable $pgclient is set to its path.
Else it is set to 0.
An option is added to the configure script for setting an search path instead of $PATH ($pgclient_dir).
If pgclient is necessary for installing your program, you can do something like
the following to stop configure with an error if pgclient wasn't found:
if test "x$pgclient" = "x0"; then AC_MSG_ERROR([We need that to setup the database!]); fi
pgclient can be found at http://pgclient.freesources.org