Calls from blocks show up as from caller method

[dylanahsmith]

This is happening for a similar reason as https://github.com/Shopify/rotoscope/issues/57

This is happening because rotoscope tries to keep information from the stack based by pushing a frame to this stack on call events and popping a stack from on a return event.

except that it doesn't keep track of calls to blocks.

Unlike that issue, this one is easier to fix with the current approach by also tracing block calls and returns so they can be included in the rotoscope stack.