tests/indent: strengthen requirements for test input files

Previously, 'indent run-equals-prev-output' was allowed even when there
was no 'indent run' section above. This created an ambiguity, since
'previous output' could mean either the 'indent run' section or the
'indent run-equals-input' section.

tests/indent: add test for left-justifying declarations

tests/indent: change directive from '#' to '//'

Using a '//' instead of '#' turns the directives into well-formed C
code, resulting in fewer error markers in the editor.

indent: remove FreeBSD IDs

Most of the IDs were empty anyway.

tests/indent: clean up and extend tests

tests/indent: normalize empty lines in tests

tests/indent: merge duplicate input/output and output/output

No functional change.

tests/lint: document and extend the tests for options

tests/indent: condense tests for bool options

Previously, each bool option such as '-bacc/-nbacc' had 6 test files:
input, options, output for the positive and negative option. Splitting
this test data into separate files made it harder than necessary to
quickly compare the test output from '-bacc' with that of '-nbacc'.

Have a single test for the positive and negative option, allowing
several tests to run on the same input with different options.

This commit only contains the rather mechanic changes of concatenating
the previous test files and inserting the '#indent' directives, which
are documented in t_options.sh. Removing duplicate input sections, as
well as other cleanups will follow soon.

No functional change.