Update, rename and clean up various scripts

Rename contrib/tools/chkfmt to contrib/tools/chkfmt.sh; refactor:
 * Increase the max line length for contrib/**/*.[ch] from 96 to 100.
 * Set the max line length for ci_*.sh to 100.
 * Use `basename $0` instead of the hard-coded script name.
 * Update comments.

Remove contrib/tools/reindent. For automated code formatting, including
indentation, we need a robust solution.

Add an empty line after the hashbang line in all scripts.

Remove the "last changed" version info from comment headers.
(The version control system maintains this information automatically.)

contrib/tools/intgamma.sh

@@ -1,13 +1,11 @@
 #!/bin/sh
-#
+
 # intgamma.sh
 #
-# Last changed in libpng 1.6.0 [February 14, 2013]
-#
 # COPYRIGHT: Written by John Cunningham Bowler, 2013.
 # To the extent possible under law, the author has waived all copyright and
-# related or neighboring rights to this work.  This work is published from:
-# United States.
+# related or neighboring rights to this work.  The author published this work
+# from the United States.
 #
 # Shell script to generate png.c 8-bit and 16-bit log tables (see the code in
 # png.c for details).
@@ -17,10 +15,10 @@
 # (0..255) value and a similar table for the exponent calculation.
 #
 # "bc" must be on the path when the script is executed, and the math library
-# (-lm) must be available
-#
-# function to print out a list of numbers as integers; the function truncates
-# the integers which must be one-per-line
+# (-lm) must be available.
+
+# Function to print out a list of numbers as integers; the function truncates
+# the integers which must be one-per-line.
 function print(){
    awk 'BEGIN{
       str = ""