docs: replace three placeholders with something that makes sense

Also, uncapitalize two arguments, to match the style of all others.

Signed-off-by: Benno Schulenberg <bensberg@telfort.nl>

man/xkb/XkbAllocGeomProps.man

@@ -32,10 +32,10 @@ XkbAllocGeomProps \- Allocate geometry properties
 .SH ARGUMENTS
 .TP
 .I geom
-_summary_
+geometry for which properties should be allocated
 .TP
 .I num_needed
-_summary_
+number of new properties required
 .SH DESCRIPTION
 .LP
 Xkb provides a number of functions to allocate and free subcomponents of a 

man/xkb/XkbChangeNames.man

@@ -22,13 +22,13 @@
 .\"
 .TH XkbChangeNames __libmansuffix__ __xorgversion__ "XKB FUNCTIONS"
 .SH NAME
-XkbChangeNames \- _summary-line_
+XkbChangeNames \- Change symbolic names in the server
 .SH SYNOPSIS
 .HP
 .B Bool XkbChangeNames
 .BI "(\^Display *" "dpy" "\^,"
 .BI "unsigned int " "which" "\^,"
-.BI "XkbDescPtr " "Xkb" "\^);"
+.BI "XkbDescPtr " "xkb" "\^);"
 .if n .ti +5n
 .if t .ti +.5i
 .SH ARGUMENTS
@@ -39,7 +39,7 @@ connection to the X server
 .I which
 mask of names or map components to be updated
 .TP
-.I Xkb
+.I xkb
 keyboard description to be updated
 .SH DESCRIPTION
 .LP

man/xkb/XkbGetNames.man

@@ -28,7 +28,7 @@ XkbGetNames \- Obtain symbolic names from the server
 .B Status XkbGetNames
 .BI "(\^Display *" "dpy" "\^,"
 .BI "unsigned int " "which" "\^,"
-.BI "XkbDescPtr " "Xkb" "\^);"
+.BI "XkbDescPtr " "xkb" "\^);"
 .if n .ti +5n
 .if t .ti +.5i
 .SH ARGUMENTS
@@ -39,7 +39,7 @@ connection to the X server
 .I which
 mask of names or map components to be updated
 .TP
-.I Xkb
+.I xkb
 keyboard description to be updated
 .SH DESCRIPTION
 .LP