Installer has incorrect URL for CSS when WordPress is in a subdirectory of the domain

[sambauers]

The installer loses the correct URL for the CSS files when WordPress is being installed in a sub-directory of the domain.

This is because site_url() returns nothing during install and the script loaders rely on site_url() to determine the full url to the CSS.

I have borrowed the URL guessing routines from elsewhere in the installer/updgrader to create a new function wp_guess_url().

I have applied this to all places where the URL is guessed (that I could find) to de-dupe the regexp code.

I'm not sure if this is occuring in the 2.5 branch, but it is happening in trunk.

Patch included.

[sambauers]

Related ticket at #4732

Closed older ticket as duplicate at #7028

[ryan]

(In [8182]) wp_guess_url() and install styling fixes from sambauers. fixes #7129 see #4732