Fix linenum calculation in xpp

First, when `begin` is parsed, the end of line `\n` is not eaten
up. In fact, there may be code following after `begin` on the same
line; this is placed after xpp in the line after `begin`. If nothing
follows the `begin` statement on the same line, an empty line is
added. This means, that `linenum` must __not__ increased here; it is
increased when the `\n` of this line is found.

Similar argument for parsing a `task` line; `linenum` must
__not__increased here as well.

Also, when processing include files, an additional '\n' was included, which
is later counted. To revert this effect, linenum has to be decreased here as
well.

When parsing `.help` ... `.endhelp` however, one `linenum` increase was
missing, which is added now.

unix/boot/spp/xpp/lexyy.c

@@ -2868,6 +2868,7 @@ do_include()
 	 * first line of include file.
 	 */
 	unput ('\n');
+	linenum[istkptr-1]--;
 
 	yypush_buffer_state(yy_create_buffer(yyin,YY_BUF_SIZE ));
         BEGIN(INITIAL);

unix/boot/spp/xpp/xpp.l

@@ -413,6 +413,7 @@ do_include()
 	 * first line of include file.
 	 */
 	unput ('\n');
+	linenum[istkptr-1]--;
 
 	yypush_buffer_state(yy_create_buffer( yyin, YY_BUF_SIZE ));
         BEGIN(INITIAL);

unix/boot/spp/xpp/xppcode.c

@@ -822,6 +822,7 @@ skip_helpblock (void)
 	    if (istkptr == 0)
 	        linenum[istkptr]++;
         }
+	linenum[istkptr]++;
 }
 
 
@@ -888,7 +889,6 @@ parse_task_statement (void)
 		if ((ch = nextch()) != '\n')
 		    unput (ch);
 	    } else if (ch == '\n') {
-		linenum[istkptr]++;
 		ntasks++;			/* end of task statement */	
 		break;
 	    } else
@@ -1153,7 +1153,6 @@ begin_code (void)
 	setcontext (BODY);
 	d_runtime (text);  outstr (text);
 	outstr ("begin\n");
-	linenum[istkptr]++;
 
 	/* Initialization. */
 	nbrace = 0;