path -> Path
removed eval.rs: dead code

@brson confirms that eval.rs is now dead code
unneccessary since tjc's commit 78ec6fe30cf2b, fixing #2804
removed test referring to WONTFIX bug #2443
libsyntax comments only
auto merge of #5709 : jbclements/rust/miscellaneous-cleanup, r=jbclements

There's no unifying theme here; I'm just trying to clear a bunch of small commits: removing dead code, adding comments, renaming to an upper-case type, fixing one test case.