Cleanup and improve source code comments

Global review, which includes the following changes to try to increase
consistency, update and improve the source code comments:

 - Spelling fixes.
 - Use American English forms.
 - Uppercase NULL, NUL and ASCII.
 - Use “Note: ” instead of the slightly cryptic “NB: ” form.
 - Write comments as proper sentences, including capitalizations and
   ending dots.
 - Move comments before the code, function or variable they refer to.
 - Move general function comments outside the body.
 - Convert function and variable description comments to doxygen.
 - Use one space before dot, exclamation and question marks.
 - Use ‘’ or “” instead of `' style quoting.
 - Remove author names from comments, already visible from “git blame”.
 - Mark strings for translators with “TRANSLATORS: ”.
 - Remove useless or outdated comments.
 - Fix comment indentation.
 - Standardize comment format:

   /* Short text comment. */

   /* Long text,
    * comment. */

   /*
    * Section text.
    */

1 files changed, 6 insertions, 6 deletions

diff --git a/m4/dpkg-compiler.m4 b/m4/dpkg-compiler.m4
index 3a3860175..65ed76863 100644
--- a/m4/dpkg-compiler.m4
+++ b/m4/dpkg-compiler.m4
@@ -52,23 +52,23 @@ AC_DEFUN([DPKG_TRY_C99],
 #include <stdbool.h>
 #include <stdio.h>
 
-/* Variadic macro arguments */
+/* Variadic macro arguments. */
 #define variadic_macro(foo, ...) printf(foo, __VA_ARGS__)
 ]],
 [[
-	/* Compound initialisers */
+	/* Compound initializers. */
 	struct { int a, b; } foo = { .a = 1, .b = 2 };
 
-	/* Trailing comma in enum */
+	/* Trailing comma in enum. */
 	enum { first, second, } quux;
 
-	/* Boolean type */
+	/* Boolean type. */
 	bool bar = false;
 
-	/* Specific size type */
+	/* Specific size type. */
 	uint32_t baz = 0;
 
-	/* Magic __func__ variable */
+	/* Magic __func__ variable. */
 	printf("%s", __func__);
 ]])], [$1], [$2])dnl
 ])# DPKG_TRY_C99