IE6 Adv. Search cross browser UI breaks

[npeterson]

IE6 is having problems with the Javascript that enables/disables the checkboxes next to each journal. See:  http://plosmedicine-demo.plos.org/search/advancedSearch.action

Here's how to reproduce it from the default state ("Only search in the following journals" option selected): 1. Select the "Search all journals" radio button. Note that the checkboxes next to each journal are not disabled - that should be. 2. Now select the "Only search in the following journals" option again. 3. Note that now the checkboxes next to each journal are disabled - the opposite of what they should be.

[ssterling]

(In [7737]) Fixes IE problem on advanced search page. The Cross-Journal checkboxes now are active or greyed-out correctly with the appropriate radio button selection.

Addresses #1321 Addresses #1327