Fixes to win32 services

There were quite a few issues with the win32 service code that this
corrects. The first is that some of the comments in the code needed
to be updated. Looks like code was copied and reused but the comments
were not updated to reflect what the reused code was doing.

There was the potential in InstallService() where not all the service
handles would be closed if errors were hit at certain spots.

Before installing a new service the old service was not uninstalled.
This is desireable in the case where the new service has different
options or points to a different path location for example. In some
cases it might be bad where some type of user change was made but that
is difficult to account for. I leaned toward cleaning up the old so that
the new service can be installed fresh.

This also causes an error when the service goes to install because the service
already exists. This would actaully happen each time the OSSEC installer was ran
but due to some incorrect logging statements (which I'll explain below) a blank
line would appear.

When doing an uninstall of a service the service wasn't stopped prior to
the uninstallation. This would leave the service running until the service
was stopped or the computer rebooted at which point the service would dissappear.
It is better to stop the service before unintsalling. I'd imagine that is what
the user would expect to happen during such an operation.

The logging in this code was not done correctly. Namely, the call to merror()
in the InstallService() function after the "install_error" label was completely
wrong and would result in a nearly blank line in the logs. There were also reports
of times where a user would install the agent on a win32 machine and everything
would work except the service would never register. Fixing all of the logging to
use verbose() should hopeflly lead to better troubleshooting of errors like that
in the future.
Merge pull request #129 from awiddersheim/fix_win32_service

Fixes to win32 services