Set close-on-exec flag in most places where file descriptors are

Set close-on-exec flag in most places where file descriptors are
opened in our libraries (in case another application thread spawns a
new process) and in the KDC programs (in case a plugin library spawns
a new process).

Checked calls to: open fopen THREEPARAMOPEN mkstemp socket accept dup
dup2 pipe.  In: util lib plugins kdc kadmin/server krb524.

The various programs are less critical than the libraries, as any
well-written plugin that spawns a new process should close all file
descriptors it doesn't need to communicate with the new process.

This approach also isn't bulletproof, as the call to set the
close-on-exec flag is necessarily a separate call from creating the
file descriptor, and the fork call could happen in between them.  So
plugins should be careful regardless of this patch; it will only
reduce the window of potential lossage should a plugin be poorly
written.  (AFAIK there are currently no plugins that spawn processes
where this would be a problem.)

Update dependencies.

ticket: 5561

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@20143 dc483132-0cff-0310-8789-dd5450dbe970