plugins/rrdtools: don't leak filename

Reported by coverity as CID #1112121
core/snmp: fix usage of pointer outside of scope

Reported by Coverity as CID #1112122
core/fsmon: fix memory leak

Reported by Coverity as CID #1100817
core/io: Fix resource leak

Reported by Coverity as CID #1100815
core/utils: fix resource leak

Reported by Coverity as CID #1100814
core/utils: fix resource leak in uwsgi_write_intfile

The more error condition you squeeze in one line the more chances
to leak :)

Reported by Coverity as CID #1100812
Merge pull request #430 from xrmx/coverity2510

Fix some leaks reported by coverity