Search symlink target directories for module when file is in a linked package

[nvenegas]

For a package foo that has a dependency on bar, when we npm link bar inside foo in npm 3+ (where nested dependencies are generally flattened into the "root" directory's node_modules, where "root" = foo's directory in this example), rather than searching inside bar/node_modules directory we should actually be searching inside foo/node_modules.

If bar's dependency isn't found inside foo/node_modules, then we should probably fall back to searching inside bar/node_modules.

And, of course, generalized for any symlinked parent structure.