speed-up session restore a little

git-svn-id: http://svn.code.sf.net/p/texstudio/code/trunk@4176 92cce386-e96d-4106-809f-596c673a3fd8
enlarge drop box

git-svn-id: http://svn.code.sf.net/p/texstudio/code/trunk@4177 92cce386-e96d-4106-809f-596c673a3fd8
speed loading of hidden documents

git-svn-id: http://svn.code.sf.net/p/texstudio/code/trunk@4178 92cce386-e96d-4106-809f-596c673a3fd8
remove callgrind commands

git-svn-id: http://svn.code.sf.net/p/texstudio/code/trunk@4179 92cce386-e96d-4106-809f-596c673a3fd8