Changed multi-line C comments into another style.

The left side doesn't look unbalanced.

src/sp65/geosicon.h

@@ -55,9 +55,9 @@
 
 StrBuf* GenGeosIcon (const Bitmap* B, const Collection* A);
 /* Generate binary output in GEOS icon format for the bitmap B. The output
- * is stored in a string buffer (which is actually a dynamic char array) and
- * returned.
- */
+** is stored in a string buffer (which is actually a dynamic char array) and
+** returned.
+*/