Continuation of 27bf7328

Previous behavior was confusing, and the code path hard to follow.
Rework, and clarify the established behavior in the appropriate man pages.

Bug 4514.

X11 implies Contain, and Contain is incompatible with NoHold as
the Extern step creation will race with the step launches.

Bug 5500.

This reverts commit dcc93022.

This reverts commit b9fb67d8.

CID 187777.
Bug 5593.

scan-build complains about this possibly being used uninitialized with
pthread_join(), but on review the path it identifies as causing that
is impossible. Initialize this anyways in the hopes of surppressing that
warning.

This also randomizes the backup controller port numbers which
were not being handled here for some reason.

Bug 5166

Bug 5426

Coverity CID 187776

Drop debugging message, full gres_alloc string is printed out already.

Rework prefix handling slightly.

Drop the debugging message here. The calling path above us prints
out the entire gres_alloc string, and I don't think it's necessary
to continue to break out the individual elements like this.

Rework the prefix (now sep) handling as well slightly.

Do a little cleanup around how the separator is handled while here.

Change _build_path to return the xmalloc()'d string, and make sure
to free it where appropriate.

Add comment about how the processing of the PATH environment variable
here is backwards from convention.

Fixes GCC 8.2.0 warnings.

Fix some -Werror=restrict and -Werror=format= issues.

Silence GCC 8.2.0 warning.

Nothing modifies this, so don't bother making a copy of it.

Related to GCC 8.2.0 compilation fixes.

Fixes GCC 8.2.0 compilation warnings.

Bug 5465.

improve some logs
correct comment formatting for linux kernel standard

this will happen if a job releases its resources to expand another job,
triggering a second epilog and slurmctld errors about cpu count underflows