JavassistHelper: do not rely on isFrozen

When classes are loaded via ClassPool#toClass, they are marked as
frozen, but not their dependency classes (even if they were modified
using Javassist, too). Hence we need to be very lenient when it comes
to defining classes after giving ij-legacy a shot.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
fiji-compat's Mighty Mouse handling moved to ij-legacy

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
fiji-compat's CompositeImage handling moved to ij-legacy

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
fiji-compat's ImagePlus handling moved to ij-legacy

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Some of fiji-compat's ij.IJ handling moved to ij-legacy

... but only the non-Fiji-specific parts.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
fiji-compat: setting the context class loader moved to ij-legacy

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
IJ1Patcher: legacy headless support moved to ImageJ2

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
IJHacker: code to set the application name moved to ImageJ2

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Organize imports in FijiClassLoader

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
fiji-compat: move NoSuchMethodError handling to ij-legacy

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Fix compiler warnings in CheckClassVersions

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Fix compiler warnings in User_Plugins

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Fix compiler warnings in FijiClassLoader

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Fix compiler warnings in fiji.Main

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Fix compiler warnings in OtherInstance

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Fix compiler warnings in SetIcon

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Fix compiler warnings in fiji.command.Command

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Fix compiler warnings in IJ_Alt_Key_Listener

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Fix compiler warnings in SimpleExecuter

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Fix compiler warnings in FileDialogDecorator

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>