tests/lint: make 'expect+-' comments stricter

Previously, the expectations from these comments were already satisfied
if the expectation occurred somewhere in the actual message from lint.
This meant that the prefix 'error:' or 'warning:' could be omitted from
the 'expect' comment. These omissions were hard to see in a manual
review. Now any omissions must be visually marked with '...'.

The test msg_342 now reports its messages properly as being in the file
msg_342.c, rather than msg_341.c. This had been a copy-and-paste
mistake.

tests/lint: expect complete messages in feature tests

Previously, the tests contained many comments like /* expect: 123 */,
which were useless to a casual reader since nobody is expected to learn
lint's message IDs by heart. Replace these with the complete
diagnostics, to show what lint is complaining about.

The tests named msg_*.c have been left unmodified since they mention the
full message text in their header comment.

No functional change.

lint: in code from included files, print stack trace

Previously, the standard NetBSD build generated several lint warnings in
lhash.h from OpenSSL, without providing any hint as to which file
actually included that header. In cases like these, lint now interprets
the line number information in the preprocessor output from GCC to
reconstruct the exact include path to the file in question.

The program check-expect.lua had to be rewritten almost completely since
it assumed that all diagnostics would come from the main file. In all
existing tests, this was true, but these tests did not cover all cases
that occurred in practice. Now it records the complete location of the
diagnostic instead of just the line number.