Remove sniffer and add entr for file watching

This works better across POSIX platforms. The lack of support for file
watching on FreeBSD (lack of FSEvents, inotify) can be tricky.

This pipes ``find(1)`` + ``grep(1)`` into ``entr`` and runs the desired
tests at our convenience.
See also: http://entrproject.org/

Author: tony

.tmuxp.yaml

@@ -12,7 +12,7 @@ windows:
   panes:
   - focus: true
   - pane 
-  - sniffer
+  - find . -type f -not -path '*/\.*' | grep -i '.*[.]py$' | entr -c ./run-tests.py
 - window_name: docs
   layout: main-horizontal
   options:
@@ -24,4 +24,4 @@ windows:
   - focus: true
   - pane
   - echo 'docs built to <http://0.0.0.0:8003/_build/html>'; python -m SimpleHTTPServer 8003
-  - sniffer
+  - find .. -print | grep -i '.*[.]rst' | entr -c make html

bootstrap_env.py

@@ -106,6 +106,13 @@ def which(exe=None, throw=True):
 
 
 def main():
+    if not which('entr', throw=False):
+        message = (
+            'entr(1) is used in this app as a cross platform file watcher.'
+            'You can install it via your package manager on most POSIX '
+            'systems. See the site at http://entrproject.org/'
+        )
+        fail(message)
     if not virtualenv_exists:
         virtualenv_bin = which('virtualenv', throw=False)