Fix some spelling errors (mostly in comments).

src/qe/qe_arith_plugin.cpp

@@ -316,7 +316,7 @@ namespace qe {
         void mk_bound_aux(rational const& a, expr* t, rational const& b, expr* s, expr_ref& result) {
             SASSERT(a.is_neg() == b.is_neg());
             expr_ref tt(t, m), ss(s, m), e(m);
-            // hack to fix wierd gcc compilation error
+            // hack to fix weird gcc compilation error
             rational abs_a(a);
             rational abs_b(b);
             if (abs_a.is_neg()) abs_a.neg();

src/qe/qe_datatype_plugin.cpp

@@ -46,7 +46,7 @@ Copyright (c) 2015 Microsoft Corporation
 //   -> \/_i R_C(t_i) & phi[t_i/x]  \/ phi[false, true]
 // 
 //  Justification: 
-//  - We will asume that each of t_i, s_j are constructor terms.
+//  - We will assume that each of t_i, s_j are constructor terms.
 //  - We can assume that x \notin t_i, x \notin s_j, or otherwise use simplification.
 //  - We can assume that x occurs only in equalities or disequalities, or the recognizer, since 
 //    otherwise, we could simplify equalities, or QE does not apply.

src/qe/qe_lite.cpp

@@ -1816,7 +1816,7 @@ namespace fm {
         }
 
         // An integer variable x may be eliminated, if
-        //   1- All variables in the contraints it occur are integer.
+        //   1- All variables in the constraints it occur are integer.
         //   2- The coefficient of x in all lower bounds (or all upper bounds) is unit.
         bool can_eliminate(var x) const {
             if (!is_int(x))

src/qe/qe_mbi.h

@@ -47,7 +47,7 @@ namespace qe {
         /**
          * \brief Utility that works modulo a background state.
          * - vars
-         *   variables to preferrably project onto (other variables would require quantification to fit interpolation signature)
+         *   variables to preferably project onto (other variables would require quantification to fit interpolation signature)
          * - lits
          *   set of literals to check satisfiability with respect to.
          * - mdl

src/qe/qe_term_graph.cpp

@@ -669,7 +669,7 @@ namespace qe {
 
             // Here we could also walk equivalence classes that
             // contain interpreted values by sort and extract
-            // disequalities bewteen non-unique value
+            // disequalities between non-unique value
             // representatives.  these disequalities are implied
             // and can be mined using other means, such as theory
             // aware core minimization