maint: enforce private symbol section sorting

maint: enforce private symbol section sorting

Automating a sorting check is the only way to ensure we don't
regress.  Suggested by Dan Berrange.

* src/check-symsorting.pl (check_sorting): Add a parameter,
validate that groups are in order, and that files exist.
* src/Makefile.am (check-symsorting): Adjust caller.
* src/libvirt_private.syms: Fix typo.
* src/libvirt_linux.syms: Fix file name.
* src/libvirt_vmx.syms: Likewise.
* src/libvirt_xenxs.syms: Likewise.
* src/libvirt_sasl.syms: Likewise.
* src/libvirt_libssh2.syms: Likewise.
* src/libvirt_esx.syms: Mention file name.
* src/libvirt_openvz.syms: Likewise.