gstrfuncs: Fix regression in C++ types accepted by g_str_equal()
Further to commit bcd364af, fix the types accepted by the
g_str_equal()
macro for C++ too. C++ is more restrictive about
const-correctness.
Add unit tests.
Signed-off-by: Philip Withnall pwithnall@endlessos.org
Fixes: #2820 (closed)
Closes #2820 (closed)