Changed H5check_version() to suppress the warning message totally if
$HDF5_DISABLE_VERSION_CHECK is 2 or higher. (Old behavior treated 3 or higher
the same as 1, that is to print a warning and allows the program to continue.
Tested:
h5committested, extra jam serial, --disable-embedded-libinfo.
Add new tests (tcheck_version, testcheck_version.sh) to verify H5check_version()
does issue warnings and abort accordingly.
Tests:
H5committed tested plus jam serial tested.