[boost] [iostreams] Check zlib/bzip2 availability on configuration checks

13 Feb 2013

      Hi all,

I attached a patch for preventing build error with the environment which
provides no zlib and/or bzip2.

This patch detects zlib.h and bzlib.h availability on configuration
checks timing. It also should work with any environment variable (e.g.
ZLIB_SOURCE,BZIP2_SOURCE, ...).

Suggestions and comments welcome.

Thanks,
Kohei Takahashi