Allow debian builds with libcurl4-gnutls-dev

The only relevant part of this package is the content of /usr/include/curl, these are the same for libcurl4-openssl-dev and libcurl4-gnutls-dev.
Fixes for deprecated libcouchbase functions
Set prefix for Client-Src-IP-Address, too
Depend on krb5-libs, not krb5
Fix previous commit... should be setting prefix on src_ipaddr field
Check for null leaf values when parsing JSON structures. Fixes #790
Fix dynamic client debug messages
fr_ipaddr_cmp should compare prefixes too 0.0.0.0/1 != 0.0.0.0/0
Set CURLOPT_NOSIGNAL in rest module

This is required for multithreaded applications (see http://curl.haxx.se/libcurl/c/libcurl-tutorial.html#Multi-threading). Once in a while, this would result in a longjump error:

    *** longjmp causes uninitialized stack frame ***: freeradius terminated
    ======= Backtrace: =========
    /lib/i386-linux-gnu/i686/cmov/libc.so.6(__fortify_fail+0x50)[0xf73b16a0]
    /lib/i386-linux-gnu/i686/cmov/libc.so.6(+0xeb60a)[0xf73b160a]
    /usr/lib/i386-linux-gnu/libcurl-gnutls.so.4(+0x8085)[0xf71bf085]

(file and memory locations may vary among platforms).

The crash occured about once or twice per hour while under continuous load, there is no definite way to reproduce it. I haven't seen it anymore with these changes after several hours of testing.
Merge pull request #793 from qnet-herwin/curl_nosignal

Set CURLOPT_NOSIGNAL in rest module
Merge pull request #789 from qnet-herwin/debian_libcurl_gnutls

Allow debian builds with libcurl4-gnutls-dev
Be more selective when we fix up prefixes for 'wildcard' clients
Remove duplicate is_wildcard() function
Be less picky about attribute names.  Closes #796
Fix typo from 97b8c9
Make pairsteal() steal only one attribute

So that we can call it from other places in valuepair.c
Only radsniff calls it for a list of VPs, so we just move
the loop to radsniff
Free unknown DICT_ATTRs.  Closes #795

The unknown DICT_ATTRs are converted to talloc, and various
sweeping changes made through the code to accomodate this.
Missed breaks
Use better ctx for dict_attrunknown
Remove vp_free entry from ATTR_FLAGS.  it's no longer needed