bidiag D&C routines

Collaboration diagram for bidiag D&C routines:

Topics
	lasd0: D&C step: top level solver
	lasdt: D&C step: tree
	lasd1: D&C step: merge subproblems
	lasd2: D&C step: deflation
	lasd3: D&C step: secular equation
	lasd4: D&C step: secular equation nonlinear solver
	lasd5: D&C step: secular equation, 2x2
	lasdq: D&C step: leaf using bdsqr
	— singular values only or factored form —
	lasda: D&C step: top level solver
	lasd6: D&C step: merge subproblems
	lasd7: D&C step: deflation
	lasd8: D&C step: secular equation

Detailed Description