Refresh and drop patches.

The following patches have been dropped:
    01-libpng15.patch
    06-remove-encoding-from-desktop-file.patch
    07-fix-spelling-errors-in-binaries.patch
    09-fix-format-security-warnings.patch
    21-fix-privacy-breach-in-doco.patch

debian/patches/19-show-text-files-with-abs-path.patch

@@ -14,10 +14,10 @@ This patch header follows DEP-3: http://dep.debian.net/deps/dep3/
  1 file changed, 18 insertions(+)
 
 diff --git a/help-dialogs.c b/help-dialogs.c
-index 3658bfc..9151d52 100644
+index 0f4e3b2..6214429 100644
 --- a/help-dialogs.c
 +++ b/help-dialogs.c
-@@ -422,6 +422,24 @@ char *find_file(char *file, size_t *size, char *lang)
+@@ -423,6 +423,24 @@ char *find_file(char *file, size_t *size, char *lang)
        lang_suffix[1] = lang[1];
     }