Initialize the context class loader to the app class loader

Previously, we initialized it to the boot class loader, but that is
inconsistent with Java; if compiling against OpenJDK's class library,
the context class loader is therefore initialized to the app class
loader, too.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Set File.pathSeparator and File.separator

Many Java programs expect those fields to be initialized to non-null
values, including SCIFIO (http://scif.io/).

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Initialize Logger instances to the 'INFO' level by default

... otherwise, logging would throw an exception when trying to
determine whether the current level allows the message to be logged.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Support Logger#log(Level,String,Object)

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Add a dummy implementation of EmptyStackException

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Implement the Math#signum method

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Fix NPE in Field#getAnnotation

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