#38 Pre-submit extension point

[David Corbin]

P4Eclipse should support a "pre-submit" extension
point. Furthermore, it should provide optional support
for automatically:
a) doing a revert -a before submitting
b) doing an Organize Import on Java files
c) doing a Format on Java files

[David Corbin]

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The basic pre-submit extension poin has been added. (really
a misnomer. It's a pre-'edit changespec'