[docs] fix $< gnuism in docs makefile

Fixes GH #1125
trace: better array traces, print size also
[test] t/stress/rpa-splice.t: reproducible testcases for GH #766

with asan:
t/stress/rpa-splice.t (Wstat: 10752 Tests: 225 Failed: 42)
  Failed tests:  11-12, 16, 36-37, 41, 61-62, 66, 81-82
                86-87, 91, 106-107, 111-112, 116, 131-132
                136-137, 141, 151-152, 156, 161-162, 166
                176-177, 181, 186-187, 191, 201-202, 206
                211-212, 216
[test] less verbose exit_code test. check $ENV{TEST_VERBOSE}
[pmc] fix splice overflows with negative count

Fixes GH #766.
Throw illegal argument with negative count arguments for now.

TODO: Implement support for negative count argument for splice.
Add more splice methods.
[pmc] harmonize and combine out of bounds exception strings

use less static string memory. no special context.
Use only "illegal argument" for unsupported negative arguments.
GH #1126

* index out of bounds,
* illegal argument (for illegal negative args),
* can't resize (for fixed*pmcs or size=0 arguments)
* StopIteration
More error message harmonization  #1126

Do not end the exception string with ".", "!" or "\n".
[pmc] allow negative array key indices

Fixes GH #1127
currently we throw "index out of bounds" when getting or setting $P0[-1]
the added code is only:
        if (key < 0)
            key += size;
so it is hard to argue for performance reasons.
ditto for resizable*array for consistency if not already implemented.
[test] change array tests to new harmonized out of bounds exceptions
ChangeLog for the 3 array changes