Fix several regressions.

* company.el:

(company--adjust-column): Account for `company-tooltip-margin' so
that tooltip lines up with prefix, `window-width' permitting.

(company-pseudo-tooltip-show): New argument HEIGHT, must be
positive integer. This function creates pseudo-tooltip with HEIGHT
lines at screen location (ROW, COLUMN); no longer depends on
position of point. Fix line padding. Set `company--point-max'
after padding new lines so `company--incremental-p' works
correctly. Don't immediately restore `buffer-modified-p', save to
`company-modified' instead . Save `buffer-chars-modified-tick' to
`company-tick'.

(company-pseudo-tooltip-show-at-point): Calculate proper `row',
`col', and `height' before calling `company-pseudo-tooltip-show'.

(company-pseudo-tooltip-edit): If we altered buffer content by
padding lines, then all tooltip lines may potentially drift, so
update overlay even when `company-line-start' is 0.

(company-pseudo-tooltip-hide): Fix "Args out of bounds" error in
empty buffers. Restore `buffer-modified-p' if
`buffer-chars-modified-tick' did not increase.

(company-pseudo-tooltip-hide-line): Don't set `[line|wrap]-prefix'
overlay property if underlying buffer line does not have prefix.

(company-pseudo-tooltip-guard): Removed.
(company-pseudo-tooltip-frontend): Check
`buffer-chars-modified-tick' instead of buffer content to
determine if redraw needed.

* company-tests.el

(company-pseudo-tooltip-show, company-pseudo-tooltip-does-not-get-displaced):
Updated.