How distcheck configuration should work

[Jeremy C. Reed]

On Wed, 16 Apr 2014, Marcin Siodelski wrote:

> This means that if you require to specify location of log4cplus to build
> Kea, the configure will go just fine, but the distcheck will fail
> complaining about the lack of log4cplus, because the --with-log4cplus
> will be dropped. If you specify --with-dhcp-mysql or --with-dhcp-pgsql
> the switches will also be silently dropped by distcheck. As a result,
> the backends will not compile and unit tests will not be run.

I sometimes use:

make distcheck DISTCHECK_CONFIGURE_FLAGS="--with-gtest=/usr/pkg --with-boost-include=/usr/pkg/include --disable-install-configurations"

We can just extend the configure.ac (and macros to set more 
FOO_DISTCHECK_CONFIGURE_FLAGS and then append to the 
DISTCHECK_CONFIGURE_FLAGS in the top-level Makefile.am.