libbson 1.2.0beta bundles yajl (seems version 2.0.4)

And use some private part of it

• yajl/yajl_parser.h and yajl/yajl_bytestack.h are not installed.
• yajl_bs_push is not exposed (objdump), perhaps other

Per Fedora Packaging Guidelines, bundled library are not allowed.
See https://fedoraproject.org/wiki/Packaging:No_Bundled_Libraries

So it will be great to see collaboration between the 2 projects, and thus allow to build libbson with system libyajl.