[ gpsdrive ] improvement to debian build rules

[Hamish]

Hi,

for rev 2289 ("Only use GDA3 if available on the system") I think the
test is broken?

for one thing apt-cache tells you if the package is available in the
distribution, not if it is installed on the system. for another thing I
am not sure the if/then statement acts as expected- it always tests as
true AFAICT.

+	if apt-cache search libgda3-dev | grep -q libgda3-dev ; echo $? ; then \
+	      cmake -DCMAKE_BUILD_TYPE=Release \
 		-DCMAKE_INSTALL_PREFIX=/usr \
...
+		-D WITH_GDA3:BOOL=OFF \

I am not totally convinced that this sort of helpful automation is
actually worth it, but.....


perhaps better:

    if dpkg -l libgda3-dev > /dev/null ; then
       echo "have GDA3-dev"
    else
       echo "do not have GDA3-dev"
    fi


also better would be to somehow follow the setting in
DefineOptions.cmake instead of deciding based on what is
installed (for users with the libgda3-dev package installed
who do not want it in the build).


In the past I have used -DWITH_GDA3=OFF there, is
"-D WITH_GDA3:BOOL=OFF" better?



Hamish