Suppress warnings

More warning suppression... After this I no longer get any warnings from clang++ with the following warning related compiler options:
`-pedantic -Wall -Wextra -Wformat-nonliteral -Wcast-align
-Wpointer-arith -Wmissing-declarations -Wcast-qual -Wshadow
-Wwrite-strings -Wchar-subscripts -Wredundant-decls`

There were warnings from istl, they have not been handled here of course, but were instead silenced using `#pragma GCC diagnostic ignored "-Wsome-warning"` within a push-pop block.