Use the solarized dark variant as the default urxvt colors; use
degraded, solarized dark variant for file/dir colors (for `ls`)

-- override default urxvt term colors with 24-bit solarized versions in Xresources
------> this provides true solarized colors in an otherwise 256-color terminal
-- alter Bash prompt (PS1) color
-- no longer force the degraded, 256-color mode for GVim and Vim
-- use dircolors-solarized theme "256dark"
------> this provides degraded solarized colors for the output of `ls`