Revert "Remove a useless threads example"

This reverts commit 6864a66cf136d05007a809f011ce3d73d17abc85.
threads/alloc_test.pir was used to disprove the rakudo threads
leakage claim.
[examples] re-add threads/alloc_test.pir with docs
Fix pod syntax errors in files written in Perl 5.
Correct POD syntax errors in POD embedded in .c, .pmc, .pir, etc files.
[test] remove stale files from t/codingstd/pmc_docs.t
[tools] correcting `rm_f` command in `make_cover.pl`

When removing `.gcov` files, the configured `rm_f` command was used.  This
unfortunately used an unexpanded `make` variable `$(PERL)` and thus was
producing errors such as:

    sh: 1: PERL: not found
    sh: 1: -MExtUtils::Command: not found

The fix was to use the configured perl value and the `ExtUtils::Command`
option as would be used within a Makefile.  This change means that what the
code intends to do (delete the `.gcov` file) actually happens and removes
the error from `make cover` output.
[travis] allow_failures for codingstd_tests

do not show them as red
Fix version number.
Prepare for the 6.2.0 release.
Tightened Changelog, since Crow stops processing on blank line.
[test] --update-fingerprint for current native pbcs

to avoid test todos
examples: improve SYNOPSIS of bench_newp.pasm
examples: add benchmarks/run.sh

sample ../bench.sh script:
make clean archclean
perl Configure.pl --optimize=-O3
make -j4 -s
make -j4 test_prep
time examples/benchmarks/run.sh

=>
master        	f8510c7: 0m44.284s
rurban/6model 	9055a9e: 0m43.407s
rurban/pmc2c_orig 	6cbf270: 0m43.767s
examples: more benchmarks

add and verify http://whiteknight.github.io/2011/05/10/timings_vtable_overrides.html
as winxed files
examples: prepare winxed pirs

 document internal src/pmc/resizablepmcarray.pmc functions
examples: add cleanup

use only parrot without -O2 in examples for better comparison with older versions
MANIFEST: add the 2 new examples/benchmarks/ files
[test] add testcase for openpip with Env GH #1065

already works. Thanks to pmichaud
[test] fix prev. test on windows. need cmd /c for pipes
[codingstd] fix DESCRIPTION for dispatch.winxed

t/codingstd/pod_description.t failed