Always explicitly set border widths on manage

Always explicitly set border widths on manage

When a window becomes managed, explicitly set the current border width
to the default instead of relying on the default value of -1 to apply
the correct value.

Now that there are two different kinds of default borders, a border
width value of -1 is ambiguous. This can lead to different border widths
effectively being applied when the container changes from tiling to
floating, which is surprising behavior.

This commit extends behavior introduced in this commit to normal
borders:

7afe9cc78b4d22dfd5a0c5866382a0e001ea38b6

Explicitly set current border width when BS_PIXEL

fixes #1304