Fix a small but stupid bug that the result of `timer_start` (i.e. the
timer ID) was evaluated as Ex command. This would lead to a jump to the
top of the file, every time the vimrc was reloaded (i.e. when a .vim is
saved).
Use `call` instead of `execute`, to fix this.
The checktime command is not available in the command line window. As
the `CheckTime` function runs every second, the command line window
spits out an error message every second making it practically unusable.
This patch silences the `checktime` call to fix this.
