Adding support to submit to coverity
Update coveralls badge, add coverity badge
remove oldstyle local_options
Use ax_check_zlib.m4 instead of PKG_CHECK_MODULES
Make zlib mandatory dependency.
fixes for compile under CYGWIN

Signed-off-by: Yucong Sun <sunyucong@gmail.com>
Merge pull request #188 from sunyc/master

Fix compiling under CYGWIN