Adds a possibility to owerwrite 'checklink' by using:
$ ac_cv_path_CHECKLINK=<path-to-executable> ./configure
Note: Specifying '/usr/bin/true' as follows:
$ ac_cv_path_CHECKLINK=/usr/bin/true ./configure
can be used to build the html documentation on machines
(usually builders) which by design disables network access
during a build process.
Signed-off-by: Damian Wrobel <dwrobel@ertelnet.rybnik.pl>
