TS-2095: replace TS_FLAG_HEADERS

TS_FLAG_HEADERS does not give any value over AC_FLAG_HEADERS, so
just remove it. Also alleviate the preprocessor warnings from the
unordered_map check.
Merge branch 'ts-3006-more-fixes' of https://github.com/shinrich/trafficserver

This closes #117
TS-3006 Generalize the read raw data routine rather than doing a cut-n-paste