Fix raw execution input reader's signal blocking.

Signals are generally blocked within threads in Bro so that the main
thread does all signal handling, however, signal masks are inherited
over fork() and exec(), so they should be unblocked before exec() so
that process can respond to signals normally.

This fixes the raw reader from leaving behind processes that didn't
respond to SIGTERM at shutdown because it was blocked before exec().
Internal UID simplifications/nits.
Fix logging filter over-allocation and leak.

The leak could happen in a couple cases where adding a log filter
fails: OOM and unsupported field type.
Fix invalid/mismatched deallocators.
Fix memory leak in DNS TXT lookups.
Adjust DNS memory leak test to actually fail if there's a leak.
Adjust HLL cluster leak test so leaks trigger a failure.
Fix memory leak if a DNS request fails to be made.

A symptom of this is a "can't issue DNS request" warning in
reporter.log. (Doesn't look like this should be a typical thing
that happens in most environments).
Fix signatures that use identifiers of type table.
Fix mem leak when unserializing an arg in a function call fails.

Shouldn't be a typical scenario since hopefully we'd know about
and fix the underlying problem w/ unserialization...
Fix mem leak when failing to end a serialization.

We'd probably know about it if that actually ever happened in practice
(which it shouldn't).
Fix mem leak when unserializing table entry fails.

Shouldn't happen in practice.
Fix mem leak when merging incompatible types.

Though this would typically be caused by a scripting error that should
be fixed and Bro would exit anyway if encountered at parse time.
Fix mem leak in failing table initialization case.

Specifically that case looked like tables that have a compound index
and an element assignment fails due to a type mismatch.
Merge branch 'master' into fastpath
Workaround type ambiguity w/ default record field.
Updating submodule.

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