Code Review request for new "jsign" tool

[Sean Mullan]

I have moved the signing code out of the "jpkg" tool and into a new "jsign" tool 
so that existing module-files can be signed. See [1] for rationale.

Here is the new command line syntax:

usage: jsign [-v] [--keystore <keystore-location>] [--storetype <keystore-type>] 
[--protected] [--tsa <url>] [--signedmodulefile <signed-module-file>] 
<module-file> <signer-alias>

Option                                  Description
------                                  -----------
-?, -h, --help                          Show this help message
-f, --signedmodulefile <File: path>     File name of signed module file
-k, --keystore <location>               URL or file name of module signer's
                                           keystore location
-p, --protected                         Do not prompt for a keystore password
-s, --storetype <type>                  Module signer's keystore type
-t, --tsa <URI: location>               URL of Time Stamping Authority
-v, --verbose                           Enable verbose output

webrev: http://cr.openjdk.java.net/~mullan/jigsaw/webrevs/jsign/webrev.00/

I encountered one issue with the module-file format [2] which should be 
addressed. Ideally, when a signature is generated over an existing module file, 
none of the contents of that module file should be modified. However, there is 
one field (the sections field in the module file header) that breaks that rule, 
because the signature itself is a section, and therefore the number of sections 
needs to be incremented by one. It may be possible to do that, but it would 
result in the code being much more complex. Thus, I would like to propose that 
this field be changed to be the number of sections following the module-info 
section (or the signature section if included), i.e. the number of sections in 
the "rest" of the module. This would not affect the Reader implementation, as it 
only uses this field to determine how many sections it needs to read in the rest 
of the module.

--Sean

[1] http://mail.openjdk.java.net/pipermail/jigsaw-dev/2011-April/001278.html
[2] http://cr.openjdk.java.net/~mr/jigsaw/notes/module-file-format/