add a --no-requirejs option or something to the compile command

[ryanramage]

Based on discussion with @caolan . Would be nice to have option to not bundle the require preamble into the jam compile.

see: https://github.com/caolan/jam/blob/master/lib/commands/compile.js#L182-L199 and https://github.com/caolan/jam/blob/master/lib/commands/compile.js#L219