ENH: Reduce number of duplicate linear algebraic operations in regression fit.
Removed one more rank issue
Changed name of extendedpinv to pinv_extended

Updated properties using decorators
Merge pull request #1092 from guyrt/streamline-linearalgebra

ENH: Avoid duplicate svd in RegressionModel
ENH: add lbfgs for fitting, but testing shows arima errors
ENH: Check that there are sufficient dof for estimation.
BUG: Never squeeze to a scalar.
ENH: Handle rare case of nobs == 1.
BUG: Don't let maxlag > nobs. Closes #1146.
TST: Add test for #1146.
Merge pull request #1149 from jseabold/fix-1146

BUG: Fix small data issues for ARIMA.
MAINT: improve compatibility with old scipy versions, but some complex number are sneaking in and causing tests to fail
MAINT: more flexibility in setting parameters for fitting
MAINT: for model fitting, let lbfgs use its own fprime approximation instead of passing a separate function that uses finite differences
MAINT: change another fitting default solver from None to 'lbfgs'
MAINT: add keyword to the kalman filter log likelihood calculation function, reducing the amount of side effects of the function when False is passed
MAINT: avoid side effects when computing log likelihood for the estimation of the score or hessian
ENH: Raise on 0,0 order models in AR(I)MA. Closes #1123
MAINT: use a mysterious args=(False,) argument instead of using nested function definition
MAINT: add conditional code to support varying versions of scipy fmin optimizers
Merge pull request #1156 from jseabold/arma00-error

ENH: Raise on 0,0 order models in AR(I)MA. Closes #1123