(#16809) Use only one record_type in cron provider

The cronprovider defines two record_types :crontab and :freebsd_special
to handle the following crontab records:

    @daily /bin/my_daily_command
    0 0 * * * /bin/my_daily_command

This has a few issues:

a)
The merging of the name (the comment before the cronentry itself) and
the environment variables only happens for the :crontab record_type
but not for the :freebsd_special record_type so information may get
lost (#16809)

b)
When parsing an existing record the record_type can be automatically
determined (depending on which regex matched) but when creating a new
entry the record_type is undefined and the default :crontab is used.
So if a new cronentry is created with the :special property set it is
still treated as a crontab entry (so the to_line hook of the :crontab
record_type is used and not of the :freebsd_special record_type)
which is kind of confusing.

c)
It is really hard to change the time of a cronentry from the special
format to a normal format (or vise versa) e.g. if we already have the
following cronentry

    # Puppet Name: foo
    * * * * * /bin/foo

and we have defined the following resource

    cron { "foo":
      special => daily,
    }

the resource is treatd as in sync because the existing cronentry is
parsed as a :crontab record_type and this record_type doesn't define a
:special field that could be out of sync

This patch now only uses one record_type that internally parses the
timefield as either the old format (minute,hour,monthday,month,weekday)
or the special format. This way the above issues go away (but the
different to_line, post_parse hooks get a bit more difficult to handle
both entries)
(#16809) Refactor crontab provider with block_eval

Ruby 1.9 was failing to parse the previous implementation of the custom
crontab record_line provider methods. This commit uses the FileParsing
block_eval syntax to attach methods to the record_line object instead of
using anonymous procs.
(#16809) Remove refs to freebsd_special cron type

The legacy test::unit crontab tests contained checks for the
freebsd_special record line. Since those were not getting run by the
normal rspec coverage it got missed when the freebsd_special line type
was removed. This commit removes the outdated references.
Merge branch 'pull-1216'

This closes GH-1216.