Fix issue #17848 (Questionable advice in bug report instructions)
Add run-pass-valgrind tests

Closes #16914
Move some tests to run-pass-valgrind
Make rpass-valgrind work with pretty
Remove support for .rc files from test.mk
Part of #6993. Moved a bunch of uses of Ident to Name
Error if we should be able to Valgrind but can't
auto merge of #17868 : nick29581/rust/valgrind, r=alexcrichton

r? @alexcrichton
auto merge of #18217 : mikedilger/rust/bug_report_instructions, r=pnkfelix

Fixed as per @pnkfelix comments in #17848
Improve code in the intro.

All these stars aren't needed anymore.
auto merge of #18253 : steveklabnik/rust/small_doc_fixes, r=huonw

All these stars aren't needed anymore.
auto merge of #17683 : gereeter/rust/ident-to-name, r=pcwalton

This does a large chunk of #6993. It is based on top of #17654.