This commit fixes issues below:

extractContent() might forward NULL to marker.
ListBucket() fogets to delete keylist when errors happen.
contents in ListBucketResult are not cleared.
downloader is not destroyed in unit tests.
get_opt_s3() and truncate_options() in unit tests need to be freed.
xmlNodeGetContent() needs to be freed.
xml.ctxt->myDoc needs to be freed.
function for the XML library needs to be cleared.

Thanks to Kuien and Valgrind.

Authors: Nikos Armenatzoglou and Shreedhar Hardikar.

Now s3ext supports all amazon s3 regions.
http://docs.aws.amazon.com/general/latest/gr/rande.html#s3_region

fix read_callback()
fix memleaks, thanks to cppcheck
check every pointer returned from malloc()
remove unused functions, add uri encoding codes
strftime()'s argument max includes the terminating null byte

compatible with s3.amazonaws.com and s3-us-east-1.amazonaws.com regions
catch any exceptions thrown by C++ functions
set min and max values of threadnum and chunksize

and will move development to GPDB source tree after this.

This is first release and doesn't support write operation.
S3 has its own unittest with gtest