Zabbix

....I..... [ZBX-5168] add missing and fix existing help_items
	   [svn merge ^/branches/2.0 -c r28576]

Next changes are included in this commit:
  - add missing internal checks to help_items
  - add vfs.file.contents to help_items
  - add third parameter to vfs.file.reg* items
  - add second parameter for perf_counter item
  - fix key formatting as per documentation