Fixed fprintf parameters in pngtoh.c

Killed warninng "format ‘%x’ expects argument of type ‘unsigned int’"
Enable Norwegian Bokmål (nb) translation

The po/nb.po file is not used by Cinelerra and ignored when doing
'make install', causing the translation to be missing in the generated
debian packages.  This patch enable it.
Generate png from _png.h file.
Use png as source, and generate _png.h file during the build.

This is the first batch of this change, transforming all the plugins.
Add picon_png.h and pngtoh to .gitignore

These files are now generated.
Change Units::format_to_separators() to return 'const char *' and not 'char *'.

The change propagate to BC_Textbox::set_separators() too.
This get rid of several warnings and bring the code closer to HV 4.5.
Make BC_WindowBase::create_xatom() use 'const char *'.

This get rid of four of these:
warning: deprecated conversion from string constant to 'char*' [-Wwrite-strings]
Make sure to print the long value from labs() using %ld.

This get rid of this warning:

bcmeter.C: In member function 'void BC_Meter::get_divisions()':
bcmeter.C:253:40: warning: format '%d' expects argument of type 'int', but argument 3 has type 'long int' [-Wformat=]
     sprintf(string, "%d", labs(current));
                                        ^
Make BC_DialogThread::lock_window() argument 'const char*'.

One lock_window() prototype was forgotten in commit
2a446f48c0ee459029572a9b40a86b0d30a610cb.  This change get rid of one
warning in cinelerra/.

  mainerror.C: In member function ‘void MainError::show_error_local(char*)’:
  mainerror.C:178:43: warning: deprecated conversion from string
   constant to ‘char*’ [-Wwrite-strings]
    lock_window("MainError::show_error_local");
Avoid useless malloc() and memory leak in mplex.c

This patch fixes the issues I found in mplex.c using Coverity and
valgrind.

The mplex.c source contain a useless malloc(1), which seem to be there
to make sure a float pointer can be relased using free() when scaling
the buffer to the required size.  But the C standard specify that
free(NULL) work fine (apparently it crashes on obsolete platforms like
PalmOS and 3BSD, neither which are relevant platforms for Cinelerra), so
it is safe to initialize the audio_temp pointer to NULL instead.  The
audio buffer memory allocated later in the code is never released on
exit.  Neither is the memory allocated to the path string.  Add code to
release it just to clean up the heap, as this is done just before main()
terminates the program, to get rid of valgrind reported leak.  In the
process I made sure to correct the path array size calculation to ignore
argv[0].  Also, move the path allocation after argument checking to
avoid having to release it if the usage() info is printed.  Finally,
include <string.h> to avoid warnings about undecleared strlen() and
strcpy().

This fixes Coverity CID 58577.  Coverity did not like assigning a one
byte buffer to float*.
Update pt_BR.po translation
Fixed compilation broken by commit 8ec64541d6d3ea

The objectfile is not make target.
Get rid of all compiler warnings for plugin swapchannels

Currently building the swapchannels plugin emits the following warning.
Fixing the warning require the 'const'-ness to propagate into
BC_MenuItem and BC_PopupMenu.  Here is a patch to do this.

make[4]: Entering directory '/usr/src/cinelerra-cv/plugins/swapchannels'
  CXX      swapchannels.lo
swapchannels.C: In member function 'char* SwapMain::output_to_text(int)':
swapchannels.C:468:11: warning: deprecated conversion from string constant to 'char*' [-Wwrite-strings]
    return "";
           ^
  CXXLD    swapchannels.la
make[4]: Leaving directory '/usr/src/cinelerra-cv/plugins/swapchannels'
Get rid of all compiler warnings for plugin titler

Currently building the titler plugin emits the following warnings.
Fixing the warnings require BC_ListBoxItem to use 'const char *'.  Here
is a patch to do this, as well as fixing the incorrect incorrect *printf
statements.
Fix all warnings in threshold plugin

Killed warnings: deprecated conversion from string constant to 'char*'
New configure option --with-lots-of-warnings

Some people, like me, want the compiler to emit warnings for all the
code it find questionable.  Others want to keep the amount of warnings
at a lower level.  This patch add a new configure option
--with-lots-of-warnings to enable more compiler warnings for those of us
that want this, while leaving the default at a lower level.
Fix Lintian warning (Debian)

This patch fixes the following lintian warnings during compilation:

W: cinelerra-cv source: debian-rules-missing-recommended-target build-arch
W: cinelerra-cv source: debian-rules-missing-recommended-target build-indep
Updated Norwegian Bokmål (nb) translation
Add return values for some functions missing it.

This reduces the amount of warnings emitted from the compiler
when compiled with -Wall, and ensure a known return value
always is returned.