Add an option to prevent the BCs from being automatically adjusted in PDE15S.
Fix typo.
Another typo..
Fix conditional statement.
Use FOURCOLLOC class for periodic eigenvalue problems.
Two changes.

1. Pass correctly the prefs to linop/eigs.
2. Add tests.
Merge remote-tracking branch 'origin/development' into feature-eigs-periodic
Merge remote-tracking branch 'origin/development' into feature-eigs-periodic
Several modifications.

1. Add a adjustPref method, used by both SOLVEBVP and CHEBOP/EIGS.
2. Modify the tests to check if the solution is of the right tech.
Changes suggested by Asgeir.

Split adjustPref into two methods: clearPeriodicBC and determinePref.
Method renaming.
Rename determinePref -> determineDiscretization. And changes on inputs/outputs, and
check if fourcolloc outside clearPeriodicBCs.
Merge branch 'development' of github.com:chebfun/chebfun into feature-eigs-periodic
Adding documentation.
Missing from previous commit.
1. Delete the TODO in CHEBOP/EIGS.
2. Documentation in CHEBOP/DETERMINEDISCRETIZATION.
Fixing a typo.
Merge branch 'feature-eigs-periodic' of github.com:chebfun/chebfun into feature-eigs-periodic
Fixing a typo, adding missing verb.
Some more minor documentation fixes.