SDS: Fix bugs in Monitor-to-User Transition

1. When transitioning from monitor to user mode with the trap enabled, the trap was latching the monitor address of the transferring branch rather than the user-mode address of the branch target.

2. When executing a BRU, BRX or BRM in monitor mode, if the effective address was in user mode, the code neglected to transition the machine to user mode. And after doing so, it is necessary to check for an armed monitor-to-user trap.

Also removed superfluous trailing blanks from lines in file.
SDS: Fix clock pulse interrupt bug

The single-instruction Clock Pulse interrupt (75 octal) may be a MIN or SKR instruction. The function rtc_inst increments (MIN) or decrements (SKR) the operand and tests for zero and generates a Clock Sync interrupt (74 octal) if so. However, the SDS 940 reference manual is incorrect; in the SKR case, the test should be if the result is negative.
SDS: Do not reload channel interlace register if already alerted

From actual monitor code, sequence used to read drum:
             EOD*  10000B   Alert Interlace
GDAC3: EOD    14202    I/O control mode EOD (mode 1)
                                        A=0  High order memory address bits
                                        Hicount=2 (Word count=04000=2KW)
             POT      GDBCL+2  Low-order memory address bits.
             RRF                    (EOD 2226) Read RAD file (mode 0)

Problem is that RRF is clearing the interlace information saved by the previous POT and sets up for a new POT. That is, in sds_io.c, mod 0 of op_eomd always assumes that a POT will follow if the channel is C or greater. Have to add tests of chan_flag.  If interlace is active, do not capture new information from this EOM/EOD.

Also removed superfluous trailing blanks from lines in file.
SDS: Various fixes to asynchronous communication mux

1. In pot_fork, the permanently asserted interrupt, the interrupt bits were assigned in the wrong order -- bit 8 is interrupt 0 and bit 23 is interrupt 017 in each group of 16. Also, the group number was incorrectly calculated -- need to subtract 0200 before dividing by 020.

2. In case 3 of EOM and SKS when in SDS mode, it does not dispatch properly. The device table is set for Genie mode.  Add test for device 077 in SDS mode and switch to device 1, which is Mux in Genie mode.

3. Add test to PIN to verify that scanner is locked before returning PIN data.

4. Mux should not queue a new interrupt for a flag type if it is already queued and pending for a different channel. If do so, when the CPU clears the interrupt, the second interrupt is lost.

5. If POT specifies interrupt but no Tx character present, queue a Tx interrupt immediately if the transmitter is not active. This technique is used by the 940 monitor to start output of the transmit character buffer.

6. Per the 940 reference manual, after servicing the highest priority interrupt on a particular channel, the scanner should look at all other channels before looking for additional interrupt types on the first channel. Change scanner to always resume scan with the Rx interrupt on the next channel from where the scanner paused.

Also removed superfluous trailing blanks from lines in file.
SDS: Fixed head disk addressing corrected when start new sector

rad_adjda was setting sba=0 at a sector boundary, which did not reflect that the first 12-bits of the sector have already be read or written. Must set sba=1 for proper addressing.

Removed superfluous end-of-line spaces from file.
SDS: Alter display and entering of ASCII data

SDS internal ASCII differs from standard external ASCII. Alter the examine and deposit functions with -A switch to properly adjust between the two forms. Also allow strings rather than one-character per word as was in the original code.  Clean up six-bit character display logic to use a loop.

Remove superfluous trailing blanks from lines in file.
SDS: Allow specifying breakpoints as being in monitor, user or normal mode only

Breakpoint logic now allows four execution-type breakpoints:
 -E  as before, break if PC equals address, unqualified by mode
 -M break if PC equals address and machine is in monitor mode
 -N break if PC equals address and machine is in normal (SDS 930) mode
 -U break if PC equals address and machine is in user mode
SDS: Adjust real-time clock pulse interrupt period

Clock is running twice as fast as it should -- 120 interrupts per second instead of 60.  Cannot find problem in initialization or calibration or count-down code, so for now, divide rtc_tps by 2 prior to invoking sim_rtcn_calb.  Now 940 Executive reports wall-clock time advancing at proper rate.
SDS: Minor additions to SDS documentation

Document new breakpoint types and display and input of packed SDS internal ASCII characters.  Add note describing memory map options for display and input discovered in code. Word change tracking enabled.