[GH #833] preload configure steps

Term::ReadLine does not work on my mingw, debugging configure steps is a pain.
E.g. "b postpone auto::snprintf::runstep" does not set a breakpoint when
debugging Configure.pl

I added a preloading of all steps into early Configure.pl so that breakpoints
can easily be set. The old handling is not changed.
[GH #833] preload only when debugging perl via -d

As per jkeenans comment https://github.com/parrot/parrot/issues/833#issuecomment-8634064
[GH #836] Improve parsing pmc2c UNUSED arguments

UNUSED(arg) amcros are now detected in pmc bodies and change the argument declaration
to SHIM().
Empty bodies with return 1; are now detected and the two args are SHIMed.
UNUSED(interp) cause a new warning to be replaced by UNUSED(INTERP).
warnings: Improve clang support

clang requires warnings overrides for -Wno-parentheses-equality
and adds -Wno-unused-result to src/ops/core_ops.c.
(used in 29582199aef9ea9462 [GH #828] Optimize print_n/i and say_n/i)
Add ccwarn::src/ops/core_ops.c SUFFIX OVERRIDE for using (void)Parrot_io_write_b

Added with 29582199aef9ea94622b4202aee129521bc
Add more UNUSED() declarations to key.pmc and core.ops
[t] Add some failing tests for #837 reported by pmichaud++
[t] Move concat tests for #837 to a more appropriate file
Revert "[t] Add some failing tests for #837 reported by pmichaud++"

This reverts commit 5d7aa2d0d7489aadc3bc3037271d919634483b90.
[GH #837] Honor encoding in imcc optimizer

Context registers unfortunately do not store type information,
just the values. We would need at least type 'U" here.
So recreate an proper const'ed encoding string from the register
value.
[cage] Remove windowism from pprof2cg.pl

use /usr/bin/perl code
Add bytebuffer resize tests for [GH #835]

As it turns out adding the failing test to t/pmc/bytebuffer.t
does not reveil any problem, but if called seperately as main it does.
Add t/pmc/bytebuffer2.t to MANIFEST
[GH #835] Fix set ByteBuffer from string

set_string_native() did not reset char* content, only the STRING *source.
[GH #837] ChangeLog line for imcc optimizer bug
[GH #837] Add benchmark to test encoding slowdown

stress_stringsu.pir tests encoding via sprintf and concat.
The fixed version is only a bit slower then the old broken version.
13.666s (broken) vs 13.506s (fixed) vs 3.022s (without encoding).

So fixing the encoding representation as STRING* in SREG and consts 'U'
is a worthwile goal.
[GH #837] New comparison benchmark against stress_stringsu.pir

Bad news:
There is almost no measurable speed advantage from ascii strings to encoded strings.
With the fix and without the fix, as sprintf handling slows down the test 4x times.

So converting a SREG and const to encoded STRING* will not gain much performance.
Merge branch 'gh837_concat'

Fixes [GH #837], a imcc optimizer problem with SREG's and const
not holding STRING*, thus no good encoding information.
Merge 'rurban/bytebuffer-resize-gh835'

Fixed conflict in ChangeLog
[GH #835] Rewrite ByteBuffer.set_string_native

Check for all needed content allocation cases. The previous version
failed when realloc'ing the content, Now use a fresh copy when needed.
[GH #835] adjust the test plan number