configure: cosmetic improvements on comments

This patch brings more consistency in the presentation of comments,
including:
 - 2 line spaces between blocks (M4 macro tend to make the file look quite
bulky, so it is making the file more aerated)
 - fixes in the length of underlining
 - adding a few comments on the reason of the check to ease maintainance

Signed-off-by: Christophe CURIS <christophe.curis@free.fr>

m4/windowmaker.m4

@@ -24,12 +24,11 @@ m4_pattern_forbid([^_?WM_])
 m4_pattern_allow([^WM_OSDEP(_[A-Z]*)?$])
 
 
-dnl
-dnl WM_CHECK_XFT_VERSION(MIN_VERSION, [ACTION-IF-FOUND [,ACTION-IF-NOT-FOUND]])
-dnl
-dnl # $XFTFLAGS should be defined before calling this macro,
-dnl # else it will not be able to find Xft.h
-dnl
+# WM_CHECK_XFT_VERSION(MIN_VERSION, [ACTION-IF-FOUND [,ACTION-IF-NOT-FOUND]])
+#
+# $XFTFLAGS should be defined before calling this macro,
+# else it will not be able to find Xft.h
+#
 AC_DEFUN([WM_CHECK_XFT_VERSION],
 [
 CPPFLAGS_old="$CPPFLAGS"
@@ -61,14 +60,14 @@ CPPFLAGS="$CPPFLAGS_old"
 ])
 
 
-dnl _WM_LIB_CHECK_FUNCTS
-dnl -----------------------
-dnl (internal shell functions)
-dnl
-dnl Create 2 shell functions:
-dnl  wm_fn_imgfmt_try_link: try to link against library
-dnl  wm_fn_imgfmt_try_compile: try to compile against header
-dnl
+# _WM_LIB_CHECK_FUNCTS
+# --------------------
+# (internal shell functions)
+#
+# Create 2 shell functions:
+#  wm_fn_imgfmt_try_link: try to link against library
+#  wm_fn_imgfmt_try_compile: try to compile against header
+#
 AC_DEFUN_ONCE([_WM_LIB_CHECK_FUNCTS],
 [@%:@ wm_fn_lib_try_link FUNCTION LFLAGS
 @%:@ ----------------------------------

m4/wm_attributes.m4

@@ -16,6 +16,7 @@
 # with this program; if not, write to the Free Software Foundation, Inc.,
 # 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 
+
 # WM_C_NORETURN
 # -------------
 #
@@ -61,8 +62,9 @@ AS_CASE([$wm_cv_c_noreturn],
         [Defines the attribute to tell the compiler that a function never returns, if the ISO C11 attribute does not work])])
 ])
 
+
 # _WM_SHELLFN_FUNCATTRIBUTE
-# ----------------------
+# -------------------------
 # (internal shell function only!)
 #
 # Create a shell function to check if we can compile with special

m4/wm_imgfmt_check.m4

@@ -16,6 +16,7 @@
 # with this program; if not, write to the Free Software Foundation, Inc.,
 # 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 
+
 # WM_IMGFMT_CHECK_GIF
 # -------------------
 #
@@ -175,7 +176,7 @@ AC_DEFUN_ONCE([WM_IMGFMT_CHECK_TIFF],
 
 
 # WM_IMGFMT_CHECK_WEBP
-# -------------------
+# --------------------
 #
 # Check for WEBP file support through 'libwebp'
 # The check depends on variable 'enable_webp' being either:

m4/wm_libexif.m4

@@ -16,8 +16,9 @@
 # with this program; if not, write to the Free Software Foundation, Inc.,
 # 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 
+
 # WM_CHECK_LIBEXIF
-# -------------
+# ----------------
 #
 # Checks the needed library link flags
 # Sets variable LIBEXIF with the appropriates flags

m4/wm_libmath.m4

@@ -16,6 +16,7 @@
 # with this program; if not, write to the Free Software Foundation, Inc.,
 # 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 
+
 # WM_CHECK_LIBM
 # -------------
 #

m4/wm_prog_cc_c11.m4

@@ -16,8 +16,9 @@
 # with this program; if not, write to the Free Software Foundation, Inc.,
 # 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 
+
 # WM_PROG_CC_C11
-# ---------------------
+# --------------
 #
 # Check if the compiler supports C11 standard natively, or if any
 # option may help enabling the support