Fix long javac commandline error

If the classpath is very long or the list of java files to compile is very
long, javac task will result in "Argument list too long" error.

This patch uses @argfiles [1] optinos to javac instead of commmand line
options.

[1] http://docs.oracle.com/javase/6/docs/technotes/tools/windows/javac.html
adding message to set HTTP_PROXY and HTTPS_PROXY for those behind a firewall
Use -- to treat filenames as non-option args to gpg.

Ordinarily I'd also check that the filename was not "-", or perhaps
get the absolute path, but in this case I know the filename. (Otherwise
this could result in a hung process as gpg waited for stdin.)
Found a couple more shell invocations.

/usr/bin/java doesn't appear to have a -- equivalent, unfortunately.
Merge pull request #983 from paraseba/long-javac-commandline

Fix long javac command line error
Merge pull request #984 from davidhc/better-errors

adding message to set HTTP_PROXY and HTTPS_PROXY if behind a firewall
Merge pull request #985 from timmc/explicit-gpg-args

Use -- to treat filenames as non-option args to gpg.
Implement `symlink?`.
Don't follow symlinks when cleaning. Fixes #988.
Print command to run a single failing test above its output.
Add experimental support for :eval-in :nrepl.
Simplify deploy

This takes advantage of the coordinate merging in pomegranate.aether/deploy.
Move prioritized picks out of meta-merge.
Pick prioritized value in add-repo if there is one
Add tests for prioritized repos.
document ns tagging and :only features of test subcommand
update test subcommand doc to have a realistic example
Merge pull request #995 from cldwalker/test-command-docs

document ns tagging and :only features of test subcommand
Perform init unconditionally
require init-ns unconditionally