Running puppet as an unpriviledged user to manage its own crontab caused
two problems under solaris:

The uid argument was passed to the execute method to set the correct uid
before executing the crontab command. The execute method has a default
argumenthash with the key :failonfail set to true. Because the suntab
filetype passed it's own hash, failonfail was nil so if crontab
completes with a non-zero exit code no error will be raised.

This is bad because running execute with :uid not only sets the correct
userid in the child process but also tries to run `Process.initgroups`
to set the correct supplementary groups of that user. This call will most
likely fail as a non priviledged user causing the whole child process to fail.

The fix now makes sure that failonfail is passed to the execute method
so failures can be handled correctly and uid is only passed if necessary
(which is not the case when the target user in the crontab resource is
the same user that is running puppet).

Since the execute method now raises an exception on non-zero exit
codes, we have to handle the case where the crontab file doesn't exist
for the user (and return '') versus other fatal errors.

Previously, there were places where a rescued exception's message was
not included in the newly raised exception. We also were not preserving
the backtrace, which makes debugging more difficult.

This commit ensures the original message and backtrace are included in
the newly raise exception.

Previously there was trailing whitespace and lines indented 4 spaces.
Just reformatted the file, no code changes.

Previously, the suntab's write method was printing the contents of the
crontab file to stdout.

This commit refactors the filetype specs to use `let`, especially the
arguments passed to the execute method.

It also adds a shared behavior for crontab file types and refactors the
suntab type to use it.

Previously, the AIX crontab filetype had the same issue as the Sun one,
the `:failonfail` argument was being set to false, so it would not raise
an error when crontab returned a non-zero exit code. The only time the
filetype raised an exception was if the command output contained the
line: 'You are not authorized to use the cron command'

This commit changes the AIX crontab filetype to raise an exception if
crontab returns a non-zero exit code.

If the user doesn't have any crontab entries, then the `#read` method
will return an empty string as is done for on Solaris.

If the command failed because the user doesn't have permission, then the
filetype will raise an exception, as it did before.

This commit also adds tests and an AIX crontab fixture.

Previously, we were calling `Tempfile#close!` which under ruby 1.8.7
will call the finalizer's cleanup routine directly. That may raise an
exception, e.g. Errno::EACCES, if the process is unable to unlink the
file, i.e. Windows. In ruby 1.9, the `Tempfile#close!` method was
changed to provide the same semantics as `#close` followed by `#unlink`.
Rather than monkey patch Tempfile, we simply call close followed by
unlink explicitly.