this allows the test suite of eWoms to be compiled on clang++ 3.8
using the following warning flags
```
-Weverything
-Wno-documentation
-Wno-documentation-unknown-command
-Wno-c++98-compat
-Wno-c++98-compat-pedantic
-Wno-undef
-Wno-padded
-Wno-global-constructors
-Wno-exit-time-destructors
-Wno-weak-vtables
-Wno-float-equal
```
without triggering warnings in opm-material or eWoms.
Note that the test-suite for opm-material does *not* yet pass without
warnings with these flags because with these flags clang likes to
complain about reducing or increasing floating point precision which
results in a formidable nightmare. I will see what I can do about
these warnings in a separate PR.
v4: properly fix the unused parameter warnings for the valgrind client
requests. thanks to [at]atgeirr for finding the issue.
93fe614558