tests: testsuite: add the --enable-long-tests argument
tests: testsuite: add the --enable-long-tests argument

The main default testsuite is intended to be "short" (less than a minute
on a standard/current development computer for the full test suite).
"Long" tests are those that can largely exceed this limit. Such long
test cases will be skipped if long tests are not enabled.

Signed-off-by: Julien Olivain <e017b3aecfdd2dc1bdcf241eeb088a15ff1e3ada@free.fr>

jolivain/glslsandbox-player,jolivain/glslsandbox-player,jolivain/glslsandbox-player,jolivain/glslsandbox-player