Keep distro packagers happy by having the option to use the system's sqlite library instead of our bundled version. Set SYSTEM_SQLITE=1 when running cmake to use the system one.
so package builders don't need local patches.
Also, instead of hardcoded firefox, use "xdg-open" or "sensible-browser"
launchers on Linux, to auto-detect user's preferred browser.
Override with cmake switch -DWEB_BROWSER=...
(Not affecting Mac/Win which are hard-coded anyway).
This patch removes the conditional compilation of ATCDCL, compiling both
the old and new ATC systems. The old system only provides ATIS, AWOS and
some dialog lookups, and hence should not conflict with the new system.
HAVE_CULLSETTINGS_CLEAR_MASK was not set, so a program to test
CLEAR_MASK was added. The Posix timer function clock_gettime is in
librt on Fedora, and probably on other systems too.
