fix for ELPA specification
Fix tip-color in pos-tip-calibrate-frame-offset

This ensures that tip-color constructed in pos-tip-calibrate-offset has
correct form, i.e., its background component is a string, rather than a lambda
that needs to be executed in order to get valid background colour.
Fix setting foreground colour when using pos-tip-show

pos-tip-show would only pass the tip-color to pos-tip-show-no-propertize,
which resulted in applying it only to frame properties by x-show-tip, but not
to the font of the tooltip itself. This seemed to work actually, but only as
long as user did not choose a custom colour theme.

Otherwise it was impossible to set text foreground colour using
pos-tip-show. (You could not just propertize the text using face as
pos-tip-show replaces the face property of the input text.)

The solution is based on how tooltip.el uses x-show-tooltip: it does set
foreground-color and background-color frame parameters, but it also
additionally applies the tooltip face to the tooltip text.
Fix problem when using pos-tip-show for the first time

When displaying first tooltip after starting Emacs, text attributes
would not be correctly applied, resulting in incorrect colour of tooltip
text and background. This would be visible only for the text, frame
foreground and background were set correctly.

This seems to have been related to the use of `make-face' to create a
temporary face for applying those text attributes. According to
documentation this function should not be used from Lisp source code. In
fact it turns out that there's no need to use a separate face at all: it
is sufficient to use a list of desired face attributes that should be
applied to text.

This fixes the problem and removes potentially costly operations
involving changing selected windows and manipulating face properties for
all the frames.
Merge branch 'fix/fg-color-and-themes'