automake cleanup: correcting binary name

Gitbuilder failed because ceph_mon_store_converter was renamed to
ceph-mon-store-converter, fixing it.

Signed-off-by: Roald J. van Loon <roaldvanloon@gmail.com>
automake cleanup: check for VTA support in gcc

VTA is unsupported in gcc < 4.5, so check compiler support for it.
This fixes builds in older distros like squeeze.

Signed-off-by: Roald J. van Loon <roaldvanloon@gmail.com>