Block alias

I'd like to suggest a minor change to the way block alias is handled in GRC.  Currently it is treated as a string.  It should be treated as 'any'.  The current approach does not scale to large flowgraphs, especially with multiple hierarchical blocks.  We should be able to set the alias based on parameters/variables.  Should be a one-line change in GRC.

While on the topic, I don't recall if gr 3.9 has finally exposed the set_block_alias on python blocks.  My old version still does not.

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Eugene Grayver, Ph.D.
Aerospace Corp., Principal Engineer
Tel: 310.336.1274
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