strip ExtJS4: add more info about `exjs.txt`

Signed-off-by: Oleg Verych <olecom@gmail.com>
strip ExtJS4: fix exit paths; fix EXTJS4 to be path with trailing slash

Signed-off-by: Oleg Verych <olecom@gmail.com>
strip ExtJS4: otherwise use `ext-all-debug.js` from same path as output/source

Signed-off-by: Oleg Verych <olecom@gmail.com>