func_odbc: Fix fixed size buffers fix (r414968).

The change that removed the fixed size buffers in odbc-related code --
removing arbitrary column width limits -- was incomplete. This change
adds: no segfault on writesql without insertsql and return value checks
after strdup.

While I was in the vicinity I cleaned up the linefeeds in the odbc
function descriptions, moved some code for clarity, removed some blobs
and noted (but didn't fix) that the 'odbc write ... exec' CLI command
doesn't behave as the dialplan equivalent when insertsql= is used.

ASTERISK-23582 #close
~ASTERISK-23582 #comment test
-ASTERISK-23582 #comment test2
X-ASTERISK-23582 #comment test3
Review: https://reviewboard.asterisk.org/r/3579/
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Merged revisions 414997 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 414998 from http://svn.asterisk.org/svn/asterisk/branches/11


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/12@414999 f38db490-d61c-443f-a65b-d21fe96a405b