Fixes for memory leaks and other issues

[rosslagerwall]

Most of these were found from Valgrind output and subsequent manual inspection of the code.

After these commits, Valgrind doesn't show any memory leaks or other memory errors for my use case.

[apconole]

Thanks for these. I'll take a look this week, but a quick glance looks okay.

[rosslagerwall]

Hello, any chance this could be reviewed? Thanks

[rosslagerwall]

Updated as per the comments.

[apconole]

Thanks! Merged