Return t if version V1 is equal to V2.
Note that version string "1" is equal to "1.0", "1.0.0", "1.0.0.0",
etc. That is, the trailing ".0"s are insignificant. Also, version
string "1" is higher (newer) than "1pre", which is higher than "1beta",
which is higher than "1alpha". Also, "-CVS" and "-NNN" are treated
as alpha versions.