OpenSystemsDevelopment / qpdf

Rather than checking consistency of libqpdf.map, generate it.

Also separate C and C++ warning flags.

Make --enable-werror work properly on msvc, handle extra warnings
flags for msvc in configure.ac instead of hardcoding into
make/msvc.mk, separate warnings flags into WFLAGS in autoconf.mk to
avoid duplication and to make it easier to override.

LARGE_FILE_TEST_PATH -> QPDF_LARGE_FILE_TEST_PATH
SKIP_TEST_COMPARE_IMAGES -> QPDF_SKIP_TEST_COMPARE_IMAGES

Update the build to support new external-libs layout, and autoconf
options to specify windows word size.  Split make_windows_releases
into multiple scripts.

For ELF systems, turn on versioned symbols by default, and add a
configure option to enable or disable them.

git-svn-id: svn+q:///qpdf/trunk@870 71b93d88-0707-0410-a8cf-f5a4172ac649

git-svn-id: svn+q:///qpdf/trunk@764 71b93d88-0707-0410-a8cf-f5a4172ac649

git-svn-id: svn+q:///qpdf/trunk@760 71b93d88-0707-0410-a8cf-f5a4172ac649

git-svn-id: svn+q:///qpdf/trunk@599 71b93d88-0707-0410-a8cf-f5a4172ac649