Updater: Fix '(unshadowing)' label

It really wanted to be a conditional.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Updater: Fix check whether a remove is unshadowing

REMOVE is not really a valid action for INSTALLED files *unless*
its current site is shadowing another one.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Updater: Fix setAction(REMOVE) when unshadowing

REMOVE is not really a valid action for INSTALLED files *unless*
its current site is shadowing another one.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Updater: unshadowing is not really removing

Therefore it should not trigger a conflict when a dependency gets
unshadowed.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Merge branch 'updater-unshadow'

These fixes were needed to be able to unshadow rsyntaxtextarea on Fiji's
update site; the shadowing version was needed for the old Script Editor
but we fixed the Editor to depend on the new version.

Pretty soon, the Script Editor will be obsoleted by ImageJ2's version,
anyway.