Detecting readline in configure

Every once in a while some user complains that "the cursor keys don't work
anymore in psql".  There has even been one case where a major vendor has
shipped binaries without readline support.  While we keep telling them,
"make sure configure finds the library and the header files", this is a
rather difficult thing for users to do reliably, especially if they are
using a pre-packaged deal where no intervention is expected.

I think we should add a --with-readline option to configure, and make
configure die with an error if the option is used and no readline is
found.  If the option is not used, readline would still be used if found.

Comments?

-- 
Peter Eisentraut   peter_e@gmx.net   http://funkturm.homeip.net/~peter