Fix compiler warnings and comment/string typos

- fix g++ warning:

> lib/checkother.cpp:3779: warning: comparison between signed and unsigned integer expressions

 - fix suncc warning (see [everything2](http://everything2.com/title/C%252B%252B%253A+static+extern+%2522C%2522)):

> "lib/checkmemoryleak.cpp", line 578: Warning (Anachronism): Formal argument __compar of type extern "C" int(*)(const void*,const void*) in call to bsearch(const void*, const void*, unsigned long, unsigned long, extern "C" int(*)(const void*,const void*)) is being passed int(*)(const void*,const void*).

- prefer empty() / isEmpty() over "size() > 0" (cases not caught by stlSize)

- fix word misspellings (mostly comments, a few output lines)

  - Parenthesis => Parentheses (both variations were used in the codebase)

  - fix typo and wording ("never alwayw") in gui/test/data/benchmark/simple.cpp's CheckOther::unsignedPositive():

```
-  "An unsigned variable will never alwayw be positive so it is either pointless or "
+  "An unsigned variable can't be negative so it is either pointless or "
```