hyphens in module names

[David Manura <dm.lua@...>]

The purpose of the following comment in the Lua Reference Manual was
not immediately clear to at least two people:

  "Moreover, if the module name has a hyphen, its prefix up to (and
including) the first hyphen is removed. For instance, if the module
name is a.v1-b.c, the function name will be luaopen_b_c."

This appears to be intended to allow multiple versions of a module to
be named without modifying their binary interface.

Having the version number be a prefix rather than a postfix is a bit
unorthodox though.