Add rpmtsLogOnce()

[ffesti]

Allows showing a log message only once.

Use in handleHdrVS. This does not add a new test case but various existing test cases fail when the NOKEY message is omited or shown more than once.

Resolves: #3336
Resolves: #3333

[pmatilai]

Pulling rpmts into the picture seems wrong to me, it limits the opportunities for using such a thing quite a lot. For example the build code doesn't have a transaction set around generally, and it'd seem weird to stick one in there for this thing's sake.

You'll want to hook it into rpmlog itself somehow. The simplest option would be just a global thing you can reset with an API call, a more flexible one would be returning a handle to both the log context and the set, and then call through that.
Something like (dunno about the names, but just to give you an idea)

• rpmlogOnce logctx = rpmlogOnceNew();
• rpmlogOnce(logctx, const char * key, int code, const char * fmt, ...)
• rpmlogOnceFree(logctx)

...and then hook that into rpmts for the effect in this particular case. The downside is that then you need to hang these context into here and there to have it available where you need it and remember to specifically call through that. So I'd just settle for a global thing inside rpmlog that you can reset at eg end of transactions and builds.

[ffesti]

Closing until the details are figured out.