As Cohsty said, the g_weapondisable cvar contains a number which tells the game which weapons to disable. I haven't got JKA code in front of me so the numbers might not be right. If say, g_weapondisable = 24, in binary this is 11000. If the game wanted to check if the saber was enabled (for this example, the bitflag for saber can be 8, or 01000 in binary), you would do:
if ( g_weapondisable.integer & WP_SABER )......
The & is a bitwise AND operator like this:
When there are two 1s in the same column, the answer is 1, otherwise its 0. The if statement checks the result in between the brackets if it's true/false. False = 0, true = anything else.
Hope that helps, and that you understood it