Bug 715172 - Consistently document Fortran's equivalent function bodies

Bug 719639 - @xrefitem with empty heading string

Some texts can be independent of \htmlonly / \latexonly

Bug 668424 - HTML links in RTF output are broken

Bug 719489 - Label "abstract" instead of "pure virtual" for Java language

Proposed patch so the word abstract is recorded correctly in case of Java

There are different types of hyperlinks: external and internal. The internal hyperlinks should have \\l behind the word HYPERLINK, the external shouldnt.

Replaced:
  if (!(x->title().length())) return;
by:
  if (x->title().isEmpty()) return;

Adjusted documentation and in case the title is the empty string in a DocXRefItem the visitPre and visitPost do nothing.

Fortran added keyword IMPURE

Added keyword IMPURE analogous to keyword PURE

Although controversioal but for consistency converted type for fortran functions to lowercase

Bug 719525 - Can't build because the definitions of ***YY_flex_debug are...

Update the documentation in respect to the version of flex and bison that can be used.

Conflicts:
	src/memberdef.cpp
	src/memberdef.h

Debug output for lexical analyzer

Adjust internationalization part to current situation

The previous commit (pull request) was missing the debug output possibility for config.l and partial for doctokinizer.l.
The later is called on different places by means of the generic definition doctokinizerYYlex, which is declared by means of YY_DECL.
To be able to add the debug output the YY_DECL had to be redefined to be a new function and the new function, with the debug output possibility, has to be called through the original function name.

Debug output for lexical analyzer

In case of error messages like:
    input buffer overflow, can't enlarge buffer because scanner uses REJECT
it is not always directly clear from which lexical analyzer (.l file) this problem comes.
This patch helps to find these problems and does the following things:
- when using the option -d lex with doxygen each time a lexical analyzer is called at the start a line like the following line will be given:
    Entering lexical analyzer: pre.l (for: ..../file.c)
  and at the end:
    Finished lexical analyzer: pre.l (for: ..../file.c)
- in case the lexical analyzer has been translated with the -d option of lex / flex the above mentioned lines will be given as part of the lexical analyzer output (to stderr) and look like:
    --entering lexical analyzer: pre.l (for: ..../file.c)
    --finished lexical analyzer: pre.l (for: ..../file.c)