Fix the test for CSV loading of non-root-level files.

I had made a bunch of misspellings. I probably fixed the actual bug when I rewrote most of condense.py.
In process_override(), stop extracting info we don't use.
Make "bases" and "derived" searches work. Ref bug 1030312.

* Make some changes to the compiler plugin's "impl" handling. Eliminate the loc fields we don't need. Rename the others to be more conventional. Leave the access specifiers for now, though we're not using them.
* process_impl() is now solely a whole-program pass and builds a global class hierarchy. Remove it from the per-file pass.
* Change needles_from_graph() to uniquify its needles. Otherwise, duplicates in the inheritance graph are possible, causing the highlighter to spit out harmless but annoying empty tags.
* Delete a bunch of now-dead code, including group_loc_name, _relate, and build_inheritance.
* SingleFileTestCase.found_lines_eq() no longer requires you to provide line numbers.
* Delete several now-invalid unit tests from test_clang. test_inheritance covers it.
* Swap the names of ParentFilter and ChildFilter, which were arguably wrong.
Label the deprecated functions unsparsify() calls as deprecated.
Clean up syntax a bit in compiler plugin.
Switch from byte-based extents to row and column offsets in the clang compiler plugin. Fix bug 1089813.

This should solve our crashes indexing the BSD userland.

Delete a bunch of redundant clang unit tests this invalidates.
Remove the now-unused offset field from Position.
Chunk bulk-index requests so they don't time out.

Add dependency on more-itertools. I keep on wanting it for things. Let's favor it over funcy when there's a choice; funcy's routines (like first()) don't tend to fail safe.
Fix buglink plugin, which crashed when enabled. Close #364.

Factor up source_page() and menu_on() to global test harness.