Fix problems related to breakpoints in packages

- Fix: Console warnings sometimes appear on package load

- Fix: It isn't possible to set a breakpoint in packages that aren't on the search path

After talking with Joe and Hadley, I believe that there is still one more fix needed to make foreign package breakpoints feel seamless: we need to set breakpoints on every copy of the function if more than one copy exists, so that the breakpoint will get hit no matter which copy is invoked. This fix is nontrivial and will require a few hours of coding and testing. If you'd prefer to wait for that fix to merge the branch, I should have it in by EOD today.