--enable-src is renamed as --enable-app. Fix build failure if
libxml2 is not available.

This will clean up resources allocated in initiate_connection()
properly.

They are just RST_STREAMed for now

We use this flag to know whether it is pushed or not

Huffman decoding is costly. It is faster to do geometric realloc
than calling nghttp2_hd_huff_decode_count to know the length in
advance.

We need jansson >= 2.5 because of s# conversion

See https://github.com/Jxck/hpack-test-case for the json file
format.

See https://github.com/Jxck/hpack-test-case for the json file
format.