added utf8 encoding line to python templates

python breaks if it encounters special characters
in files without specified encoding.
Which is especially funny if you've got umlauts
in your name.
uninstalled import: Adding overlooked exception handling around imports.
core: making block_registry thread-safe for multiple flowgraphs to access it.
Merge branch 'maint'
runtime: (dup of e0f9a39 for 3.7 structure) making block_registry thread-safe for multiple flowgraphs to access it.
runtime: 2 threading issues with the shared memory system.

1. Making a global mutex for the VM circular buffers to use and lock for multiple top_blocks to handle accessing the memory.

2. Catch the bad_alloc exception once and retry. After 1., this rarely happens unless the thread count gets large (> 20 as an estimate).
grc: fix usage of file descriptor source/sink
analog: fixed agc3_cc_impl GCC assumption
runtime: 2 threading issues with the shared memory system.

1. Making a global mutex for the VM circular buffers to use and lock for multiple top_blocks to handle accessing the memory.

2. Catch the bad_alloc exception once and retry. After 1., this rarely happens unless the thread count gets large (> 20 as an estimate).
Merge branch 'maint'
Merge branch 'master_vmcircbuf_mutex'
Merge branch 'master' of git.gnuradio.org:gnuradio
runtime: removing mutex locks; broke other things more important than what it fixed.
runtime: ignore last commit. Problem was an extra lock inside the test routine that shouldn't have been there.
Merge remote-tracking branch 'ncorgan/agc3_cc_impl_fix'
analog: fixup whitespace in agc3_cc_impl.cc
cmake: for the GnuradioConfig cmake helper function, only set the most important components as required.
controlport: added support for complex data types.

Vectors of complex are still passed as interleaved. Single values can be passed as GNURadio::complex. ControlPort can translate these in GNU Radio to gr_complex; Python programs need to convert themselves. gr-ctrl-monitor updated to handle this.

multiply_const_cc block updated to export get and set of k value through ControlPort.
Update revision to 3.7.0rc0
runtime: fixed checks on vmcircbuf file and mutex locking for creation and usage of vmcrcbuf classes.