multiple changes, expand extended description for more

- add stuff from build prerequirements dmg
- remove scilab binaries before cleaning in case they have been built
buggily and can't be used to clean things themselves properly
- whitespace and formatting
- incorporate changes from Fink's pending update to their scilab
package:
http://cvs.snaggledworks.com/viewvc.cgi/fink/3rdparty/main/finkinfo/sci/
scilab.info?view=markup
- only use the `-no_compact_linkedit` linker flag on OS X versions
before Lion
- switch more linker flags to be passed in `-Wl,` style
- remove some swig checks that caused errors
- Try using the Accelerate framework as a backup for blas on OS X

Change-Id: I7428da2fd4a0097b4fb39f76a716e7f71baea847