librustc: Fix translation of cross-crate inline or generic methods with explicit self. rs=blocking-snapshot

They shouldn't matter but there have been errors on Macs so logging
them may help root cause the issue.

1) Check for eof (shouldn't happen, but if it does we'll fall into an
infinite loop).
2) Use fatal instead of assert (will work if NDEBUG is ever defined
and provides better diagnostics).
3) Ignore errors from close since they shouldn't matter.

Closes #3679.

This commit adds a lower-level implementation of the generic
`insert_with_key` which I expect to be faster. Now insert could be
defined with insert_with_key, too, although I'm not sure we want to do that.

This also clarifies the tests a bit and adds an `insert_with` function.

Method isn't used. See discussion on #2738 and #4031

Closes #2738

Closes #3683

Minor refactoring, no review.

Closes #2739

Closes #3996

Inline numeric operations for floats.

Fix a bug where read(buf, len) would fail if buf was big enough and ...

Fix a bug where read(buf, len) would fail if buf was big enough and succeed if it was too small ... which is the opposite of correct. 

r=brson

This allows more errors to be non-fatal, as per #1871.

I only went through and started changing span_fatal to span_err in
check.rs. There are probably more errors that could be made
non-fatal. So if you see derived type errors appearing from now on,
file a bug!

r=graydon

Closes #1871

This allows the deserializer to be used on an already
parsed json object.