si-wijesekera.mim: updated to be compliant with SLS1134:2011

[Harshula]

Hi Mike,

Sahan (CC'd) pointed out to me that the si-wijesekera.mim has not been 
updated to be compliant with the latest SLS1134:2011 standard and 
there's a problem with touching letter support. I've made the relevant 
changes.

The original author of si-wijesekera.mim, Takahashi (CC'd), has reviewed 
my changes and he has recommended pushing the commits to master. They 
have been pushed:
http://git.savannah.nongnu.org/cgit/m17n/m17n-db.git/log/

Sahan also pointed out that SLS1134's spelling of the keyboard layout is 
"Wijesekara" and NOT "Wijesekera". Is there a wider impact of this name 
change outside of m17n? I've created a separate branch for it:
http://git.savannah.nongnu.org/cgit/m17n/m17n-db.git/log/?h=rename-wijesekera-to-wijesekara

Thanks,
Harshula