ITS#8118 dosearch: flush stdout

ITS#8118 dosearch: flush stdout

The LDIF output wasn't being explicitly flushed. In certain scenarios,
such as piping the output of a persistent ldapsearch to node.js v0.12
on Mac OS X 10.10.3, the output is unavailable to the process
consuming the search results until the stdio buffer fills (8192 bytes
for example). This can leave the tail end of persistent search results
in the buffer for a long time (until enough output has accumulated).

Explicitly call flush so that the output is immediately available.