The list of unsafe functions currently consists of sprintf, vsprintf,
strcat, strncat and gets.

Subsequently, some existing code needed updating to avoid warnings on
this.

Allow configure builds to generate src/config-win32.h

Skip checksrc on src/config-win32.h contents already checked at lib/config-win32.h

Allow multiple -W in checksrc.pl

We use "if(condition) {" with a space between the close paren and the
open brace.

Source files given with relative paths do not have the
-D directory specifier prepended.

Source files given with absolute paths do not have the
-D directory specifier prepended.

Useful when a known file just doesn't comply and there's no intention to
make it do so.

It now scans multiple files and outputs an error+warning count summary
at the end in case at least one was detected.

-D can be used to specify in which dir the files are located

The script now scans for conditions that starts with a space for
if/while/for lines.

By the use of a the new lib/checksrc.pl script that checks that our
basic source style rules are followed.