ask for more warnings during a Travis CI build

.travis.yml: add 'touch .devel configure'
Coverity: add the build script used by Travis-CI and Coverity Scan

from https://scan.coverity.com/scripts/travisci_build_coverity_scan.sh
Coverity: customize the build script

- add a 'Verify Coverity Scan run condition' step to avoid multiple runs wit
  Travis matrix.
- add a 'Verify Coverity Scan script test mode' step. if true no uploading,
  avoid reaching the quota. usual processing: false.
- send 'description' as VERSION#SHA (e.g.: 1.6.0-PRE-GIT#c661f8b)
Coverity: update .travis.yml for analysis by pushing in 'coverity_scan' branch
In activate routines, don't pre-set the status; set it for all errors.

This fixes some cases where it wasn't being set properly or at all, and
also means that, as it's not being set initially, compilers that do any
dataflow analysis and report uninitialized variables, and static
analyzers, should report cases where we aren't setting variables correctly.

See GH #352.
Always return 0 on a successful activation.
Merge remote-tracking branch 'bpf/master'

bpf.tcpdump.org and GitHub have diverged again.
Return warning indications from the activate routine.

Initialize the status variable to "no error or warning" (0); set it for
all error or warning conditions.  Return that variable if we haven't
failed.
Don't discard warnings.

If we've set status to a PCAP_WARNING_ value, don't use it to store the
return value of any function afterwards.
Add LINKTYPE_EPON/DLT_EPON.

Also add some missing elements to the dlt_choices[] table, and move the
entry for DLT_DBUS where it belongs (in order by type).
In activate routines, don't set status unless a warning or error occurs.

This makes the code a bit clearer, as you don't have to worry about the
status variable accidentally being set to an inappropriate value,
overriding a warning that's been put there.
In activate routines, don't set status unless a warning or error occurs.

This makes the code a bit clearer, as you don't have to worry about the
status variable accidentally being set to an inappropriate value,
overriding a warning that's been put there.
Coverity: Put 'notification_email: tcpdump-workers@lists.tcpdump.org' in comment