Fixes test for empty $PERLBREW_HOME variable.
Fixes test for perlbrew arguments in fish shell

Previously the error "test: unexpected argument at index 2: 'perl-5.18.2'" was reported when perlbrew was called with `perlbrew switch perl-5.18.2`. By interpolating the arguments into a string test receives a single argument rather than an array of arguments.
Fixes perlbrew off when using fish shell

Previously this should report that perlbrew was successfully turned off, but would in fact not do so. Since the PERLBREW_PATH variable was not cleared it would be at the front of PATH and thus perlbrew's perl would be picked up first.
"perlbrew download stable" now works as one expects

That is, it looks for and downloads the latest stable tarball, much as
```perlbrew install stable``` installs the latest stable version.
Merge pull request #379 from tgt/patch-3

Fixes perlbrew off when using fish shell
Merge pull request #376 from tgt/patch-1

Fixes test for empty $PERLBREW_HOME variable.
Merge pull request #378 from tgt/patch-2

Fixes test for perlbrew arguments in fish shell
Merge pull request #383 from RsrchBoy/topic/resolve-stable-in-download

"perlbrew download stable" now works as one expects
minor documentation touch
update changelog with list of related pull requests.
#92380: download of perlbrew fails when ca certs are not up-to-date
fix #92379: don't check ca cert on download
Merge branch 'no-cert-check' into HEAD