Components that are not installed by bower should be left alone

Some people want to be able to mix local versions of components with ones bower installs, e.g. putting a modified version of jquery into b_c. If you do this and have components that depend on jquery then every time you `bower install` or `bower update`, your custom version will be deleted and overwritten with the regular version.

While I know this is not a common case, it is very frustrating for people who try it and we don't *need* to make it impossible.