Fix collection of typos and grammar mistakes in docs and comments

Author: Justin Pryzby
Discussion: https://postgr.es/m/20190330224333.GQ5815@telsasoft.com

doc/src/sgml/ref/create_index.sgml

@@ -181,7 +181,7 @@ CREATE [ UNIQUE ] INDEX [ CONCURRENTLY ] [ [ IF NOT EXISTS ] <replaceable class=
        </para>
 
        <para>
-        Currently, the B-tree and the GiST index access methods supports this
+        Currently, the B-tree and the GiST index access methods support this
         feature.  In B-tree and the GiST indexes, the values of columns listed
         in the <literal>INCLUDE</literal> clause are included in leaf tuples
         which correspond to heap tuples, but are not included in upper-level

src/backend/jit/llvm/llvmjit_inline.cpp

@@ -9,7 +9,7 @@
  * for an external function is found - not guaranteed! - the index will then
  * be used to judge their instruction count / inline worthiness. After doing
  * so for all external functions, all the referenced functions (and
- * prerequisites) will be imorted.
+ * prerequisites) will be imported.
  *
  * Copyright (c) 2016-2019, PostgreSQL Global Development Group
  *

src/backend/optimizer/plan/planner.c

@@ -118,7 +118,7 @@ typedef struct
 
 /*
  * Temporary structure for use during WindowClause reordering in order to be
- * be able to sort WindowClauses on partitioning/ordering prefix.
+ * able to sort WindowClauses on partitioning/ordering prefix.
  */
 typedef struct
 {

src/backend/utils/hash/dynahash.c

@@ -817,7 +817,7 @@ hash_destroy(HTAB *hashp)
 	{
 		/* allocation method must be one we know how to free, too */
 		Assert(hashp->alloc == DynaHashAlloc);
-		/* so this hashtable must have it's own context */
+		/* so this hashtable must have its own context */
 		Assert(hashp->hcxt != NULL);
 
 		hash_stats("destroy", hashp);

src/interfaces/libpq/fe-auth.c

@@ -879,7 +879,7 @@ pg_fe_sendauth(AuthRequest areq, int payloadlen, PGconn *conn)
 		case AUTH_REQ_SSPI:
 
 			/*
-			 * SSPI has it's own startup message so libpq can decide which
+			 * SSPI has its own startup message so libpq can decide which
 			 * method to use. Indicate to pg_SSPI_startup that we want SSPI
 			 * negotiation instead of Kerberos.
 			 */