[PATCH] Capture user buffers with user_buffer_hex

[Craig Ringer <craig@2ndquadrant.com>]

Hi

The set of patches listed below adds new functions user_buffer_hex and
buffer_hex for the uconversions and conversions tapsets respectively. A few
helper variants are added too.

These functions allow systemtap scripts to capture and output easily parsed
userspace data in hexadecimal format.

I'd like to add another helper that prints the buffer, with an optional
prefix, without releasing the lock on the output stream so it can't get
interleaved with other output from concurrent probes. But I got a bit
bogged doing that so I'll see about submitting a separate patch for it.

To apply it you'll need to first apply another patch that reworks the tests
a little.

Prereq: https://sourceware.org/bugzilla/show_bug.cgi?id=27185
Patch: https://sourceware.org/bugzilla/show_bug.cgi?id=27187

I also wrote a small unrelated docs patch to cover the CONTEXT var for
embedded C, here: https://sourceware.org/bugzilla/show_bug.cgi?id=27186

-- 
 Craig Ringer                   http://www.2ndQuadrant.com/
 2ndQuadrant - PostgreSQL Solutions for the Enterprise