metrics: add missing exit on error path

Fixed null pointer dereference.

Reported by Coverity as CID #1127337
plugins/servlet: Check uwsgi_jvm_exception return value

Reported vy Coverity as CID #1125169.
plugins/xslt: fix memory leak

Reported by Coverity as CID #1125168
plugins/xslt: fail early if content_type is null

Fixes null pointer dereference.

Reported by Coverity as CID #1125161
core: fix memory leak

Reported by Coverity as CID #1100819
plugins/corerouter: fix memory leak

While at it reindent the code

Reported by Coverity as CID #1100818.
core: fix memory leak

Reported by Coverity as CID #1100813.
core/logging: if we cannot reopen the log exit

This fixes passing negative fds to write and lseek.

Reported by Coverity as CID #1100807.
fixed async queue full condition in goroutine mode
removed matheval flag, added generic matheval plugin and startin 1.9.20 development cycle
removed snapshotting old feature
added simple math routing actions
added simple math and concat to placeholders
added %t and %T magic vars
added %k magic vars (number of cpu cores)
implemented goroutines timeout
improved gccgo signal handling and added --timer and --rbtimer commodity options
Merge pull request #449 from xrmx/coverity0911-2

More coverity fixes
return after grace_them_all
sanitize gccgo environment