blocks: plateau_detector_fb is now a gr_block and forecasts

The detector actually could return 0 with insufficient input.
The forecast always requires at least 2*d_max_len.
However, forecast could be conditionalized to only
require this based on the last threshold detected.
runtime: export list of msg connections when performance counters are enabled
runtime: update gr-perfmonitor-x to display message ports - currently they do not show any performance statistics
Merge remote-tracking branch 'osh/master'
blocks: fix borked global search and replace
blocks: fix erroneous linkage to gr-filter (#547)
Merge branch 'maint'
cmake: convert CRLF to LF in in some modules (fixes #549)
Merge branch 'maint'