s4-param: +foo syntax

[tridge at samba.org]

Hi Metze,

 > Wouldn't it be clearer to use 'server services += openchange'?

we discussed that, but were concerned about moving away from standard
.ini file syntax in case other parsers/editors are used.

 > '+' might be a valid character in the list items.

note that we created two types of lists, P_LIST and P_CMDLIST. P_LIST
is only used for things where + and - makes sense.

The ones where + and - might be used (eg. shell commands) use
P_CMDLIST, which doesn't have this syntax change.

Cheers, Tridge