Improve code quality by enabling more compiler warnings

[diederik]

The quality of the code could be improved by enabling more compiler warnings, and fixing that code.

The most useful one (which currently is not enabled) is:

• -Wold-style-cast - a warning is issued whenever a C-style (type) cast is performed instead of C++-style x_cast<type>() casts.

And less relevant for now:

• -Wfatal-errors
• -pedantic

[valerio]

I think "boom" :P

[diederik]

Enabled all except for:

• -pedantic
• -Wfatal-errors

[valerio]

The only warning I got is about the use of preprocessor "#warning"s.

[diederik]

The warnings don't seam to add much value. Instead I've sent a request to Coverity to be included in their free Open Source scans. We could also install the KDE source code checker ('Krazy') too :)

[valerio]

The only useful warning is 'old-style-cast' which generates thousands of warnings in our SVN code.

The others are pretty useless indeed; I suggest enabling old-style-cast alongside a major code reformatting - maybe with the help of some automatic code reformatter.