Option to disable reprinting

There should be an option that disables reprinting (and the initial cloning), since normally it's only needed when working without a sourcemaps capable client. For instance, when normally developing and checking on Chrome I don't really care if the generated sources are close to the original version or it's just a blob of minified code.

This would solve some of the performance issues (ie: https://github.com/benjamn/recast/pull/133) when using the library but still guarantee that if we want to generate a properly printed version it's just toggling a flag in the build system.

No file or test is named. Start by tracing where reprinting and initial cloning occur in the build system, and review the performance context in PR #133. Done means a build-time flag can disable both operations while preserving the existing properly printed output when enabled.

Written by the indexing model from the issue text.