taskmgr: minor fixes

Created an attachment (id=7603)
Fix for this bug.

The attached patch will apply these fixes:

1) Use of CheckDlgButton() and IsDlgButtonChecked() rather than SendMessage, it will improve code readability.

2)Removes an useless initialization into perfpage.c

3) GetWindowLong/SetWindowLong were replaced with GetWindowLongPtr/SetWindowLongPtr, but GWL_WNDPROC and GWL_ID were not with GWLP_WNDPROC and GWLP_ID.

4) Corrected some comment texts.

Sincerely,

Carlo Bramini