There are 3 kinds of frames:
- java language frames
- frames for methods declared native in java. We have started to call these
  'java native'
- frames for native functions. EG, a C function called from
  a 'java native' frame. We have started to call these 'native native'.

The JVM[DT]I spec uses the terms:
 - Java programming language methods
 - JNI methods
 - native methods
 - 'not a Java programming language method'

in various places. This should be cleaned up so that a uniform
terminology is used for the 3 types of frames and what can/cannot
be done with them is clearly specified, eg:
- which kind can be used in PopFrame and NotifyFramePop(only java?)
- which kind can be used in GetFrameLocation (java and java native ?)
  - for java native, what is returned in the 'location' field?
- Others?