* Add tests for source file searching.

* Fix slash handling in tests on Windows.

* Fix test cleanup, it was leaving stale files.

* Fix number of args in Fatalf call

weblist output disassembly now contains inlined source.

In addition, fixed the line number assigned to instructions from inlined calls.

As an illustration, see the before and after output for a "pprof -weblist" command for a simple function:

[before](https://ghemawat.github.io/scratch/tmp/list1.html)
[after](https://ghemawat.github.io/scratch/tmp/list2.html)

Note that in the "before" page, the 7.26 second line cannot be expanded, but in the "after" page clicking on it reveals a wealth of information.