Merge branch 'release-1.3' into build
Build with libjpeg/libpng automatically
Links libcurl automatically
Checks zlib availability with libpng, workaround for MinGW build
Update .travis.yml
Update .travis.yml
Update .travis.yml
Update .travis.yml
Don't use system pkg-config if $cross_compile == "yes"
Use $PKG_CONFIG environment variable instead of $have_pkg_config
Don't check pkg-config availability if $cross_compile == yes
Update .travis.yml
Update .travis.yml
Don't terminate configure process if --with-libcurl=auto
Merge branch 'build' into release-1.3