optparse: fix incorrect error message when invalid short option is grouped with valid short options

[grondo]

As described in #1179, optparse error message for unrecognized option is not correct when an invalid short option is used and grouped with one or more valid options.

Fix this by assuming an invalid short option when optopt != '\0' and use the char in optopt as the unrecognized option in the error output. Otherwise, assume a long option and use argv [optind-1] as the invalid option to display.

Simple tests were also added to ensure valid error messages for unrecognized short options, grouped and ungrouped.

[coveralls]

Coverage increased (+0.04%) to 78.203% when pulling 71a46ad on grondo:issue#1179 into 9c860d0 on flux-framework:master.

[garlick]

This error is popping up in travis, in unrelated code. Not sure what to make of it.

make[4]: Entering directory `/home/travis/build/flux-framework/flux-core/flux-core-0.8.0-88-gb9d062d2/_build/sub/src/common/libsubprocess'
  CC       zio.lo
  CC       subprocess.lo
../../../../../src/common/libsubprocess/subprocess.c:1092:19: error: passing an
      object that undergoes default argument promotion to 'va_start' has
      undefined behavior [-Werror,-Wvarargs]
    va_start (ap, item);
                  ^
../../../../../src/common/libsubprocess/subprocess.c:1085:66: note: parameter of
      type 'sm_item_t' (aka 'enum sm_item') is declared here
subprocess_manager_set (struct subprocess_manager *sm, sm_item_t item, ...)

[grondo]

they did just update the trusty images recently, so perhaps a new warning in a small compiler update?

Actually this is a real error, apparently passing any value with a default type promotion before the ellipsis in a variadic function is a no-no. E.g. in this case the enum is promoted to an integer type and I guess isn't exactly defined what the size of the type would be.

Will have to find a quick fix.

https://www.securecoding.cert.org/confluence/display/cplusplus/EXP58-CPP.+Pass+an+object+of+the+correct+type+to+va_start

[codecov-io]

Codecov Report

Merging #1183 into master will decrease coverage by 0.03%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1183      +/-   ##
==========================================
- Coverage   77.82%   77.78%   -0.04%     
==========================================
  Files         158      158              
  Lines       29255    29257       +2     
==========================================
- Hits        22768    22758      -10     
- Misses       6487     6499      +12

Impacted Files	Coverage Δ
src/common/liboptparse/optparse.c	88.48% <100%> (+0.03%)	⬆️
src/common/libflux/mrpc.c	85.15% <0%> (-1.18%)	⬇️
src/common/libkvs/kvs_watch.c	86.34% <0%> (-0.89%)	⬇️
src/common/libflux/future.c	88.61% <0%> (-0.5%)	⬇️
src/common/libflux/message.c	80.94% <0%> (-0.36%)	⬇️
src/broker/overlay.c	71.67% <0%> (-0.35%)	⬇️
src/broker/module.c	83.28% <0%> (-0.28%)	⬇️
src/modules/kvs/kvs.c	63.16% <0%> (-0.27%)	⬇️
src/common/libkvs/kvs.c	65.08% <0%> (-0.26%)	⬇️
src/common/libflux/response.c	84.55% <0%> (ø)	⬆️
... and 4 more

[coveralls]

Coverage increased (+0.03%) to 78.192% when pulling badc987 on grondo:issue#1179 into 9c860d0 on flux-framework:master.

[grondo]

Rebased on current master, so we should make it through travis this time.

[coveralls]

Coverage decreased (-0.03%) to 78.135% when pulling aed7f57 on grondo:issue#1179 into ea1f316 on flux-framework:master.

[grondo]

One build hit a variant of #1169. Restarting.

[garlick]

Thanks!