Merge branch 'maint'

core: when reseting buffers, make sure that the read/write pointers are always algined.

This fixes problems when disconnecting and reconnecting blocks to a flowgraph.

core: fixed point sin/cos generator properly folds frequencies outside nyquist range to alias signal.

core: empty gr_hier_block2 contructor for virtual inheritance

gruel: created common swig include file

This work taken from gruel_work_squashed

• Language independent exception handler
• Wrapper for python calls that may block

• More common swig code, less copy pasta
• Wrapper for blocking python calls handles...