Ensure counts generated in manager_show_dialplan_helper are correct

When manager_show_dialplan_helper was written, the counter increment
for the total number of contexts was placed with the extensions
increment instead of in the enclosing loop.  This function should
now generate correct context counts.

(closes issue AST-970)
Reported-by: John Bigelow
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Merged revisions 372337 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 372338 from http://svn.asterisk.org/svn/asterisk/branches/10
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Merged revisions 372340 from http://svn.asterisk.org/svn/asterisk/branches/11


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@372344 65c4cc65-6c06-0410-ace0-fbb531ad65f3