(PUP-1426) Disallow Puppet SSL autodefenestration

The puppet cert command supports an '--all' and a '--signed' flag so
that operations take take a list of values can operate on matching
values without having to enumerate them. However these options would
also apply to the 'clean' and 'revoke' actions. This means that
accidentally running `puppet cert clean --all` promptly and without
warning revokes and then removes all certificates. In other parlance,
this kills the CA.

Because this command is extremely dangerous and doesn't have any sane
use cases that we could determine, this commit disallows using
'--signed' or '--all' with the 'clean' or 'revoke' options. If this
functionality is needed we can add a '--force' flag to allow this
operation later.
(PUP-3282) Remove support for method access to variables in ERB templ.

This removes the deprecated support to produce lookup of variable
names when a missing method was invoked having the same name as
the variable.

This is now an error, just like calling any other missing method.
(PUP=2563) Remove 1.8.7 explanatory comments from acceptance tests
(PUP-2563) Remove fix for pup-2478, which was 1.8-specific
(PUP-2563) Update quickstart.md for which rubies puppet supports
(PUP-2563) Remove 1.8 dependencies from Gemfile
(PUP-2563) Remove 1.8.7 support
(PUP-2563) Remove 1.8.7 monkey patches

This leaves some monkey patches related to 1.8.7 but tied to other
code removals (rdoc, activerecord). It also leaves in a couple that
I wasn't sure about, so there may be more monkey patches to prune.
(PUP-2563) Update unicode.md to reflect a post-1.8 world
(PUP-2563) Remove workarounds for 1.8 behavior for hash.selecdt
(PUP-2563) Revert "(PUP-3682) Disable HTTP keepalive in webrick on 1.8.7"

This was 1.8-specific fix so can be reverted.

This reverts commit 8461eb4870c4e3dbe823ede29134abad207b7249.
(PUP-2563) Remove incorrect comment about select!
(PUP-2563) Remove workaround for 1.8.7 not having ordered hashes
(PUP-2563) Remove comment about 1.8.7
(PUP-2563) Remove spec tests for pre-1.8.7 monkey patch (code was removed long ago)
(PUP-2563) Remove 1.8-specific spec test
(PUP-2563) Enable a spec test (and remove comment that conflicted with the impl)
(PUP-2563) Remove 1.8.7 conditional
(maint) Fix a spec test that may never have worked
(maint) Rename spec test to _spec.rb so it isn't skipped