- `LLFirSessionCache.sourceCache` can contain library and library
sources sessions. However, global source modification events should
not remove such sessions from the cache, because they belong to
"stable" modules.
- The commit introduces the term "stable module" as a combined term for
binary and library source modules. Library sources are not binaries,
but nevertheless they cannot cause nor be affected by out-of-block
modification.
- The term "source modules" as used by global "source" modification is
slightly imprecise, as it does *not* include library sources, but for
the sake of conciseness, I don't plan to change that.
Marco Pennekamp
24045067bf