Add fault tolerance features to djpeg and jpegtran

- Enable progress reporting at run time using a new -report argument
  (cjpeg now supports that argument as well)
- Limit the allowable number of scans using a new -maxscans argument
- Treat warnings as fatal using a new -strict argument

This mainly demonstrates how to work around the two issues with the
JPEG standard described here:
https://libjpeg-turbo.org/pmwiki/uploads/About/TwoIssueswiththeJPEGStandard.pdf
since those and similar issues continue to be erroneously reported as
libjpeg-turbo bugs.

djpeg.1

@@ -1,4 +1,4 @@
-.TH DJPEG 1 "13 November 2017"
+.TH DJPEG 1 "18 December 2019"
 .SH NAME
 djpeg \- decompress a JPEG file to an image file
 .SH SYNOPSIS
@@ -190,6 +190,19 @@ number.  For example,
 .B \-max 4m
 selects 4000000 bytes.  If more space is needed, an error will occur.
 .TP
+.BI \-maxscans " N"
+Abort if the JPEG image contains more than
+.I N
+scans.  This feature demonstrates a method by which applications can guard
+against denial-of-service attacks instigated by specially-crafted malformed
+JPEG images containing numerous scans with missing image data or image data
+consisting only of "EOB runs" (a feature of progressive JPEG images that allows
+potentially hundreds of thousands of adjoining zero-value pixels to be
+represented using only a few bytes.)  Attempting to decompress such malformed
+JPEG images can cause excessive CPU activity, since the decompressor must fully
+process each scan (even if the scan is corrupt) before it can proceed to the
+next scan.
+.TP
 .BI \-outfile " name"
 Send output image to the named file, not to standard output.
 .TP
@@ -197,6 +210,9 @@ Send output image to the named file, not to standard output.
 Load input file into memory before decompressing.  This feature was implemented
 mainly as a way of testing the in-memory source manager (jpeg_mem_src().)
 .TP
+.BI \-report
+Report decompression progress.
+.TP
 .BI \-skip " Y0,Y1"
 Decompress all rows of the JPEG image except those between Y0 and Y1
 (inclusive.)  Note that if decompression scaling is being used, then Y0 and Y1
@@ -210,6 +226,12 @@ decompression scaling is being used, then X, Y, W, and H are relative to the
 scaled image dimensions.  Currently this option only works with the
 PBMPLUS (PPM/PGM), GIF, and Targa output formats.
 .TP
+.BI \-strict
+Treat all warnings as fatal.  This feature also demonstrates a method by which
+applications can guard against attacks instigated by specially-crafted
+malformed JPEG images.  Enabling this option will cause the decompressor to
+abort if the JPEG image contains incomplete or corrupt image data.
+.TP
 .B \-verbose
 Enable debug printout.  More
 .BR \-v 's