Support srvany's AppEnvironment registry value.

Support srvany's AppEnvironment registry value.

Allow setting one or more environment variables for the application by
creating the AppEnvironment value of type REG_MULTI_SZ.  Each string
should be of the form KEY=VALUE.  VALUE may be omitted to set an empty
environment variable but the equals sign must be present.

This support is for compatibility with srvany.  In accordance with the
documented behaviour of srvany, only environment variables specified in
AppEnvironment will be passed to the service.  Any other variables, even
system variables such as %PATH%, will be ignored if they are not
explicitly listed.

Note that Windows supports adding environment variables to the service's
existing environment by creating the Environment value (also of type
REG_MULTI_SZ) under HKLM\SYSTEM\CurrentControlSet\Services\<service>
instead.  It is recommended that new services use this standard
functionality rather than AppEnvironment.

Thanks Rob Sharp.